Fixes problems with windows:

- Changed cPlayer:OpenWindow to accept a ref, tolua adds a nil check
- Close open lua window in destructor, to avoid dangling pointers

src/BlockEntities/BrewingstandEntity.cpp

@@ -65,7 +65,7 @@ bool cBrewingstandEntity::UsedBy(cPlayer * a_Player)
 	{
 		if (a_Player->GetWindow() != Window)
 		{
-			a_Player->OpenWindow(Window);
+			a_Player->OpenWindow(*Window);
 		}
 	}