Prevents a potential cross-lock deadlock. The UI thread would lock the
scene's mutex in obs_scene_atomic_update, then the item would lock the
graphics context to create a texture. Meanwhile in the video thread, it
could lock the graphics context in the render loop, then lock the
scene's mutex when rendering. When doing anything graphics-related, the
graphics context is always supposed to be locked before the scene's
mutex is supposed to be locked (it's designed that way), and the
obs_scene_atomic_update would just bypass that.
Currently if you have a scene, "Scene" for example, and you create a new
scene, the dialog will pop up with a default name, but it'll start with
"Scene 1" instead of "Scene 2". Same thing occurs with sources. This
fixes that to start from 2 instead.
