Issues on multithreading

[Bastiaan Olij]

Reported on our IRC channel a while back, I don't have more detailed info yet but capturing it so it is not lost.

There are issues when Godot is set to run the rendering in a separate thread, someone suggested it may have to do with Glad/the blit shader being created in the wrong context as a result. I'm not very familiar with the threading issues here so anyone who has ideas, please make some suggestions :)