ENGINES: Add error handling for GMM Gamestate Load/Save Usage.

As indicated by wjp, the Global Main Menu (GMM) did not check or report
on the returned error state from saveGameState() and loadGameState() usage.
This corrects this and adds a MessageDialog report of any failure.

engines/dialogs.cpp

@@ -227,19 +227,24 @@ void MainMenuDialog::save() {
 		Common::String result(_saveDialog->getResultString());
 		if (result.empty()) {
 			// If the user was lazy and entered no save name, come up with a default name.
-			Common::String buf;
 			#if defined(USE_SAVEGAME_TIMESTAMP)
 			TimeDate curTime;
 			g_system->getTimeAndDate(curTime);
 			curTime.tm_year += 1900; // fixup year
 			curTime.tm_mon++; // fixup month
-			buf = Common::String::format("%04d.%02d.%02d / %02d:%02d:%02d", curTime.tm_year, curTime.tm_mon, curTime.tm_mday, curTime.tm_hour, curTime.tm_min, curTime.tm_sec);
+			result = Common::String::format("%04d.%02d.%02d / %02d:%02d:%02d", curTime.tm_year, curTime.tm_mon, curTime.tm_mday, curTime.tm_hour, curTime.tm_min, curTime.tm_sec);
 			#else
-			buf = Common::String::format("Save %d", slot + 1);
+			result = Common::String::format("Save %d", slot + 1);
 			#endif
-			_engine->saveGameState(slot, buf);
-		} else {
-			_engine->saveGameState(slot, result);
+		}
+
+		Common::Error status = _engine->saveGameState(slot, result);
+		if (status.getCode() != Common::kNoError) {
+			Common::String failMessage = Common::String::format(_("Gamestate save failed (%s)! "
+				  "Please consult the README for basic information, and for "
+				  "instructions on how to obtain further assistance."), status.getDesc().c_str());
+			GUI::MessageDialog dialog(failMessage);
+			dialog.runModal();			
 		}
 
 		close();
@@ -256,7 +261,7 @@ void MainMenuDialog::load() {
 
 	_engine->setGameToLoadSlot(slot);
 
-	if (slot >= 0)		
+	if (slot >= 0)
 		close();
 }
 

engines/engine.cpp

@@ -420,12 +420,16 @@ void Engine::openMainMenuDialog() {
 	// (not from inside the menu loop to avoid
 	// mouse cursor glitches and simliar bugs,
 	// e.g. #2822778).
-	// FIXME: For now we just ignore the return
-	// value, which is quite bad since it could
-	// be a fatal loading error, which renders
-	// the engine unusable.
-	if (_saveSlotToLoad >= 0)
-		loadGameState(_saveSlotToLoad);
+	if (_saveSlotToLoad >= 0) {
+		Common::Error status = loadGameState(_saveSlotToLoad);
+		if (status.getCode() != Common::kNoError) {
+			Common::String failMessage = Common::String::format(_("Gamestate load failed (%s)! "
+				  "Please consult the README for basic information, and for "
+				  "instructions on how to obtain further assistance."), status.getDesc().c_str());
+			GUI::MessageDialog dialog(failMessage);
+			dialog.runModal();
+		}
+	}
 
 	syncSoundSettings();
 }