Fix weirdness in a specific rom loading scenario (fixes #2024)

Without this commit, choosing "Cancel" from a tool form's "Save changes?" dialog
(i.e. AskSaveChanges) while trying to load a rom from `File` > `Recent ROM`
would treat that recent rom as though it were missing. With this commit, an OSD
message is displayed instead.
This isn't the best fix. The return value from LoadRomInternal isn't even used
anywhere apart from LoadRomFromRecent, which is the only place the new out param
is used.

src/BizHawk.Client.EmuHawk/MainForm.cs

@@ -2019,9 +2019,10 @@ private void LoadRomFromRecent(string rom)
 			// if(ioa is this or that) - for more complex behaviour
 			string romPath = ioa.SimplePath;
 
-			if (!LoadRom(romPath, args))
+			if (!LoadRom(romPath, args, out var failureIsFromAskSave))
 			{
-				Config.RecentRoms.HandleLoadError(romPath, rom);
+				if (failureIsFromAskSave) OSD.AddMessage("ROM loading cancelled; a tool had unsaved changes");
+				else Config.RecentRoms.HandleLoadError(romPath, rom);
 			}
 		}
 
@@ -3507,9 +3508,11 @@ private string ChoosePlatformForRom(RomGame rom)
 		private LoadRomArgs _currentLoadRomArgs;
 		private bool _isLoadingRom;
 
-		public bool LoadRom(string path, LoadRomArgs args)
+		public bool LoadRom(string path, LoadRomArgs args) => LoadRom(path, args, out _);
+
+		public bool LoadRom(string path, LoadRomArgs args, out bool failureIsFromAskSave)
 		{
-			if (!LoadRomInternal(path, args))
+			if (!LoadRomInternal(path, args, out failureIsFromAskSave))
 				return false;
 
 			// what's the meaning of the last rom path when opening an archive? based on the archive file location
@@ -3523,8 +3526,9 @@ public bool LoadRom(string path, LoadRomArgs args)
 		}
 
 		// Still needs a good bit of refactoring
-		private bool LoadRomInternal(string path, LoadRomArgs args)
+		private bool LoadRomInternal(string path, LoadRomArgs args, out bool failureIsFromAskSave)
 		{
+			failureIsFromAskSave = false;
 			if (path == null)
 				throw new ArgumentNullException(nameof(path));
 			if (args == null)
@@ -3554,6 +3558,7 @@ private bool LoadRomInternal(string path, LoadRomArgs args)
 
 				if (!Tools.AskSave())
 				{
+					failureIsFromAskSave = true;
 					return false;
 				}