Blenderplayer: Setting G.main to NULL after it's freed to avoid issues later with GPU_free_images()

source/gameengine/GamePlayer/ghost/GPG_ghost.cpp

@@ -408,6 +408,7 @@ int main(int argc, char** argv)
 
 	// We load our own G.main, so free the one that initglobals() gives us
 	free_main(G.main);
+	G.main = NULL;
 
 	IMB_init();