Correct Named SaveState Dialog so it writes .State to the user's file if they forget. And improved file dialog selection for Named SaveState to allow filtering for .State and All files.

BizHawk.Client.EmuHawk/MainForm.cs

@@ -1662,6 +1662,9 @@ namespace BizHawk.Client.EmuHawk
 			}
 
 			var sfd = new SaveFileDialog();
+            sfd.AddExtension = true;
+            sfd.DefaultExt = "State";
+            sfd.Filter = "Save States (*.State)|*.State|All Files|*.*";
 			var path = PathManager.GetSaveStatePath(Global.Game);
 			sfd.InitialDirectory = path;
 			sfd.FileName = PathManager.SaveStatePrefix(Global.Game) + "." + "QuickSave0.State";