implement ClearSaveRam in gambatte core, and fix a bug with using memory domains before any frames have been run

BizHawk.Emulation/Consoles/Nintendo/Gameboy/Gambatte.cs

@@ -161,6 +161,22 @@ namespace BizHawk.Emulation.Consoles.GB
 			LibGambatte.gambatte_loadsavedata(GambatteState, data);
 		}
 
+		/// <summary>
+		/// reset cart save ram, if any, to initial state
+		/// </summary>
+		public void ClearSaveRam()
+		{
+			int length = LibGambatte.gambatte_savesavedatalength(GambatteState);
+			if (length == 0)
+				return;
+
+			byte[] clear = new byte[length];
+			for (int i = 0; i < clear.Length; i++)
+				clear[i] = 0xff; // this exactly matches what gambatte core does
+
+			StoreSaveRam(clear);
+		}
+
 
 		public bool SaveRamModified
 		{
@@ -278,9 +294,10 @@ namespace BizHawk.Emulation.Consoles.GB
 				CachedMemory = new byte[length];
 
 				writeneeded = false;
-				readneeded = false;
+				// needs to be true in case a read is attempted before the first frame advance
+				readneeded = true;
 			}
-
+	
 			bool readneeded;
 			bool writeneeded;
 

BizHawk.MultiClient/MainForm.cs

@@ -3436,8 +3436,7 @@ namespace BizHawk.MultiClient
 				if (Global.Emulator is LibsnesCore)
 					((LibsnesCore)Global.Emulator).StoreSaveRam(sram);
 				else if (Global.Emulator is Gameboy)
-					// todo: i don't like this at all.  there's no guarantee that a 0-filled sram is even an accurate clear?
-					throw new Exception("Please fix me!");
+					((Gameboy)Global.Emulator).ClearSaveRam();
 				else
 					Array.Copy(sram, Global.Emulator.ReadSaveRam, Global.Emulator.ReadSaveRam.Length);
 			}