fix exception when destruction occurs before game has been initialized

Torch/VRageGame.cs

@@ -312,7 +312,7 @@ namespace Torch
 
         private void Destroy()
         {
-            _game.Dispose();
+            _game?.Dispose();
             _game = null;
 
             MyGameService.ShutDown();
@@ -462,6 +462,7 @@ namespace Torch
         public void SignalDestroy()
         {
             _destroyGame = true;
+            if (_game is not null)
                 SignalStop();
             _commandChanged.Set();
         }