Fix up Nullable<IntPtr> brain damage

It'd be one thing if we needed a sentinel value distinct from IntPtr.Zero but we don't.  It's a pointer, and 0 is globally understood to be The Bad Value.

Some brain damage remains:
* LoadLibrary abstraction also returns Nullable<IntPtr>
* I named it `Resolve` and not `GetProcAddr` because I didn't want to see win32 everywhere I went :(

src/BizHawk.BizInvoke/BizExvoker.cs

@@ -95,9 +95,19 @@ namespace BizHawk.BizInvoke
 				}
 			}
 
-			public IntPtr? GetProcAddrOrNull(string entryPoint) => EntryPoints.TryGetValue(entryPoint, out var ret) ? ret : (IntPtr?) null;
+			public IntPtr GetProcAddrOrNull(string entryPoint)
+			{
+				EntryPoints.TryGetValue(entryPoint, out var ret);
+				return ret;
+			}
 
-			public IntPtr GetProcAddrOrThrow(string entryPoint) => GetProcAddrOrNull(entryPoint) ?? throw new InvalidOperationException($"could not find {entryPoint} in exports");
+			public IntPtr GetProcAddrOrThrow(string entryPoint)
+			{
+				var ret = GetProcAddrOrNull(entryPoint);
+				if (ret == IntPtr.Zero)
+					throw new InvalidOperationException($"could not find {entryPoint} in exports");
+				return ret;
+			}
 		}
 
 		static readonly Dictionary<Type, DelegateStorage> Impls = new Dictionary<Type, DelegateStorage>();

src/BizHawk.Common/IImportResolver.cs

@@ -10,7 +10,7 @@ namespace BizHawk.Common
 	/// <seealso cref="PatchImportResolver"/>
 	public interface IImportResolver
 	{
-		IntPtr? GetProcAddrOrNull(string entryPoint);
+		IntPtr GetProcAddrOrNull(string entryPoint);
 
 		/// <exception cref="InvalidOperationException">could not find symbol</exception>
 		IntPtr GetProcAddrOrThrow(string entryPoint);
@@ -32,7 +32,7 @@ namespace BizHawk.Common
 			_p = OSTailoredCode.LinkedLibManager.LoadOrThrow(OSTailoredCode.IsUnixHost ? ResolveFilePath(dllName) : dllName);
 		}
 
-		public IntPtr? GetProcAddrOrNull(string entryPoint) => OSTailoredCode.LinkedLibManager.GetProcAddrOrNull(_p, entryPoint);
+		public IntPtr GetProcAddrOrNull(string entryPoint) => OSTailoredCode.LinkedLibManager.GetProcAddrOrNull(_p, entryPoint);
 
 		public IntPtr GetProcAddrOrThrow(string entryPoint) => OSTailoredCode.LinkedLibManager.GetProcAddrOrThrow(_p, entryPoint);
 
@@ -84,7 +84,7 @@ namespace BizHawk.Common
 			Environment.SetEnvironmentVariable("PATH", envpath, EnvironmentVariableTarget.Process);
 		}
 
-		public IntPtr? GetProcAddrOrNull(string procName) => OSTailoredCode.LinkedLibManager.GetProcAddrOrNull(HModule, procName);
+		public IntPtr GetProcAddrOrNull(string procName) => OSTailoredCode.LinkedLibManager.GetProcAddrOrNull(HModule, procName);
 
 		public IntPtr GetProcAddrOrThrow(string procName) => OSTailoredCode.LinkedLibManager.GetProcAddrOrThrow(HModule, procName);
 
@@ -106,16 +106,23 @@ namespace BizHawk.Common
 			_resolvers = resolvers.ToList();
 		}
 
-		public IntPtr? GetProcAddrOrNull(string entryPoint)
+		public IntPtr GetProcAddrOrNull(string entryPoint)
 		{
 			for (var i = _resolvers.Count - 1; i != -1; i--)
 			{
 				var ret = _resolvers[i].GetProcAddrOrNull(entryPoint);
-				if (ret != null) return ret.Value;
+				if (ret != IntPtr.Zero)
+					return ret;
 			}
-			return null;
+			return IntPtr.Zero;
 		}
 
-		public IntPtr GetProcAddrOrThrow(string entryPoint) => GetProcAddrOrNull(entryPoint) ?? throw new InvalidOperationException($"{entryPoint} was not found in any of the aggregated resolvers");
+		public IntPtr GetProcAddrOrThrow(string entryPoint)
+		{
+			var ret = GetProcAddrOrNull(entryPoint);
+			if (ret == IntPtr.Zero)
+				throw new InvalidOperationException($"{entryPoint} was not found in any of the aggregated resolvers");
+			return ret;
+		}
 	}
 }

src/BizHawk.Common/OSTailoredCode.cs

@@ -34,7 +34,7 @@ namespace BizHawk.Common
 		{
 			int FreeByPtr(IntPtr hModule);
 
-			IntPtr? GetProcAddrOrNull(IntPtr hModule, string procName);
+			IntPtr GetProcAddrOrNull(IntPtr hModule, string procName);
 
 			/// <exception cref="InvalidOperationException">could not find symbol</exception>
 			IntPtr GetProcAddrOrThrow(IntPtr hModule, string procName);
@@ -61,17 +61,18 @@ namespace BizHawk.Common
 
 			public int FreeByPtr(IntPtr hModule) => dlclose(hModule);
 
-			public IntPtr? GetProcAddrOrNull(IntPtr hModule, string procName)
+			public IntPtr GetProcAddrOrNull(IntPtr hModule, string procName)
 			{
 				var p = dlsym(hModule, procName);
-				return p == IntPtr.Zero ? (IntPtr?) null : p;
+				return p;
 			}
 
 			public IntPtr GetProcAddrOrThrow(IntPtr hModule, string procName)
 			{
 				_ = dlerror(); // the Internet said to do this
 				var p = GetProcAddrOrNull(hModule, procName);
-				if (p != null) return p.Value;
+				if (p != IntPtr.Zero)
+					return p;
 				var errCharPtr = dlerror();
 				throw new InvalidOperationException($"error in {nameof(dlsym)}{(errCharPtr == IntPtr.Zero ? string.Empty : $": {Marshal.PtrToStringAnsi(errCharPtr)}")}");
 			}
@@ -104,13 +105,19 @@ namespace BizHawk.Common
 
 			public int FreeByPtr(IntPtr hModule) => FreeLibrary(hModule) ? 0 : 1;
 
-			public IntPtr? GetProcAddrOrNull(IntPtr hModule, string procName)
+			public IntPtr GetProcAddrOrNull(IntPtr hModule, string procName)
 			{
 				var p = GetProcAddress(hModule, procName);
-				return p == IntPtr.Zero ? (IntPtr?) null : p;
+				return p;
 			}
 
-			public IntPtr GetProcAddrOrThrow(IntPtr hModule, string procName) => GetProcAddrOrNull(hModule, procName) ?? throw new InvalidOperationException($"got null pointer from {nameof(GetProcAddress)}, error code: {GetLastError()}");
+			public IntPtr GetProcAddrOrThrow(IntPtr hModule, string procName)
+			{
+				var ret = GetProcAddrOrNull(hModule, procName);
+				if (ret == IntPtr.Zero)
+					throw new InvalidOperationException($"got null pointer from {nameof(GetProcAddress)}, error code: {GetLastError()}");
+				return ret;
+			}
 
 			public IntPtr? LoadOrNull(string dllToLoad)
 			{

src/BizHawk.Emulation.Cores/Consoles/Nintendo/N64/NativeApi/mupen64plusVideoApi.cs

@@ -61,7 +61,8 @@ namespace BizHawk.Emulation.Cores.Nintendo.N64.NativeApi
 			GFXReadScreen2 = mupen64plusApi.GetTypedDelegate<ReadScreen2>(GfxDll, "ReadScreen2");
 			GFXReadScreen2Res = mupen64plusApi.GetTypedDelegate<ReadScreen2Res>(GfxDll, "ReadScreen2");
 			var funcPtr = OSTailoredCode.LinkedLibManager.GetProcAddrOrNull(GfxDll, "GetScreenTextureID");
-			if (funcPtr != null) GFXGetScreenTextureID = (GetScreenTextureID) Marshal.GetDelegateForFunctionPointer(funcPtr.Value, typeof(GetScreenTextureID));
+			if (funcPtr != IntPtr.Zero)
+				GFXGetScreenTextureID = (GetScreenTextureID) Marshal.GetDelegateForFunctionPointer(funcPtr, typeof(GetScreenTextureID));
 		}
 
 		public void GetScreenDimensions(ref int width, ref int height)

src/BizHawk.Emulation.Cores/Waterbox/PeRunner.cs

@@ -108,7 +108,8 @@ namespace BizHawk.Emulation.Cores.Waterbox
 				var pointers = entries.Select(e =>
 				{
 					var ptr = imports.GetProcAddrOrNull(e);
-					if (ptr != null) return ptr.Value;
+					if (ptr != IntPtr.Zero)
+						return ptr;
 					var s = $"Trapped on unimplemented function {moduleName}:{e}";
 					Action del = () =>
 					{
@@ -1104,7 +1105,7 @@ namespace BizHawk.Emulation.Cores.Waterbox
 			}
 		}
 
-		public IntPtr? GetProcAddrOrNull(string entryPoint) => _modules[0].GetProcAddrOrNull(entryPoint); // _modules[0] is always the main module
+		public IntPtr GetProcAddrOrNull(string entryPoint) => _modules[0].GetProcAddrOrNull(entryPoint); // _modules[0] is always the main module
 
 		public IntPtr GetProcAddrOrThrow(string entryPoint) => _modules[0].GetProcAddrOrThrow(entryPoint);
 

src/BizHawk.Emulation.Cores/Waterbox/PeWrapper.cs

@@ -304,9 +304,19 @@ namespace BizHawk.Emulation.Cores.Waterbox
 			}
 		}
 
-		public IntPtr? GetProcAddrOrNull(string entryPoint) => ExportsByName.TryGetValue(entryPoint, out var ret) ? ret : (IntPtr?) null;
+		public IntPtr GetProcAddrOrNull(string entryPoint)
+		{
+			ExportsByName.TryGetValue(entryPoint, out var ret);
+			return ret;
+		}
 
-		public IntPtr GetProcAddrOrThrow(string entryPoint) => GetProcAddrOrNull(entryPoint) ?? throw new InvalidOperationException($"could not find {entryPoint} in exports");
+		public IntPtr GetProcAddrOrThrow(string entryPoint)
+		{
+			var ret = GetProcAddrOrNull(entryPoint);
+			if (ret == IntPtr.Zero)
+				throw new InvalidOperationException($"could not find {entryPoint} in exports");
+			return ret;
+		}
 
 		public void ConnectImports(string moduleName, IImportResolver module)
 		{