Fix rendering options failures following rP24228
Two issues are fixed:
- Atlas on non-Mac crashed when started from within the game.
- MSAA options crashed if enabled on startup.
The underlying issues where improper shutdown, and assuming the renderer was initialised than it might not be (in particular, the post-processor wasn't).
Tested by: Stan
Differential Revision: https://code.wildfiregames.com/D3131