Address screensaver video/audio not stopping on game launch

Recent reports of specific configurations or versions changing some of the event handling order, resulting in the screensaver video/audio not stopping when a game is launched from it.

Can't replicate on my end, but these changes should be harmless for the current setup, and should help with that scenario. To be fair, it should have been there from the get go - it's just pure luck that things worked until now, as the screensaver was being halted before this code would run.

es-app/src/SystemScreenSaver.cpp

@@ -511,6 +511,10 @@ void SystemScreenSaver::launchGame()
 {
 	if (mCurrentGame != NULL)
 	{
+		//Stop screensaver
+		mStopBackgroundAudio = true;
+		stopScreenSaver();
+
 		// launching Game
 		ViewController::get()->goToGameList(mCurrentGame->getSystem());
 		IGameListView* view = ViewController::get()->getGameListView(mCurrentGame->getSystem()).get();