Fix NRE when enumerating archive members to HawkArchiveFileItems

SharpCompress does this for .tar.gz it seems

src/BizHawk.Client.Common/SharpCompressArchiveFile.cs

@@ -39,10 +39,17 @@ namespace BizHawk.Client.Common
 			entryStream.CopyTo(stream);
 		}
 
-		public List<HawkArchiveFileItem> Scan()
+		public List<HawkArchiveFileItem>? Scan()
 		{
-			var files = EnumerateArchiveFiles();
-			return files.Select((e, i) => new HawkArchiveFileItem(e.Key.Replace('\\', '/'), e.Size, i, i)).ToList();
+			List<HawkArchiveFileItem> outFiles = new();
+			var entries = EnumerateArchiveFiles().ToList();
+			for (var i = 0; i < entries.Count; i++)
+			{
+				var entry = entries[i];
+				if (entry.Key == null) return null;
+				outFiles.Add(new HawkArchiveFileItem(entry.Key.Replace('\\', '/'), entry.Size, i, i));
+			}
+			return outFiles;
 		}
 	}
 }

src/BizHawk.Common/HawkFile/HawkFile.cs

@@ -102,11 +102,12 @@ namespace BizHawk.Common
 						_extractor = DearchivalMethod.Construct(path);
 						try
 						{
-							_archiveItems = _extractor.Scan();
+							_archiveItems = _extractor.Scan() ?? throw new NullReferenceException();
 							IsArchive = true;
 						}
 						catch
 						{
+							Console.WriteLine($"Failed to scan file list of {FullPathWithoutMember}");
 							_archiveItems = null;
 							_extractor.Dispose();
 							_extractor = null;
@@ -132,6 +133,12 @@ namespace BizHawk.Common
 				if (_extractor != null)
 				{
 					var scanResults = _extractor.Scan();
+					if (scanResults == null)
+					{
+						Console.WriteLine($"Failed to scan file list of {FullPathWithoutMember}");
+						Exists = false;
+						return;
+					}
 					for (int i = 0, l = scanResults.Count; i < l; i++)
 					{
 						if (string.Equals(scanResults[i].Name, autobind, StringComparison.InvariantCultureIgnoreCase))

src/BizHawk.Common/HawkFile/IHawkArchiveFile.cs

@@ -9,6 +9,7 @@ namespace BizHawk.Common
 	{
 		void ExtractFile(int index, Stream stream);
 
-		List<HawkArchiveFileItem> Scan();
+		/// <returns><see langword="null"/> on failure</returns>
+		List<HawkArchiveFileItem>? Scan();
 	}
 }