Fix: Crash when failing to load a game into a dedicated server at startup

Using the -g switch

src/openttd.cpp

@@ -2189,6 +2189,7 @@ void GameLoop()
 	if (_switch_mode != SM_NONE && !HasModalProgress()) {
 		SwitchToMode(_switch_mode);
 		_switch_mode = SM_NONE;
+		if (_exit_game) return;
 	}
 
 	IncreaseSpriteLRU();