add another check for game being unloaded before calling load callback

[Jamiras]

https://discord.com/channels/476211979464343552/757767535293890682/1280531659812507732

[CasualPokePlayer]

I'm not quite satisfied by this. This doesn't solve the underlying race condition occurring. rc_client_free_game needs to occur while there is no chance for another thread to interact with the client's rc_client_game_info_t. Or more frankly, you should not be reading client->game outside of the client->state.mutex lock. That, or you need to ensure client->game wouldn't suddenly be set to NULL and free'd while another thread is using it via some other mechanism.

[Jamiras]

Made another pass. The client->state.load object is no longer detached at the start of rc_client_activate_game. If client->state.load->game is client->game, rc_client_unload_game will no longer free it, allowing rc_client_activate_game to do so after calling its callback.