Blender Git Loki

Screen: simplify internal logic for new full-screen areas

Creating a new full screen area had it's area initialized as empty,
updating the screen then set the area to a 3D view (as a fallback),
before the actual area type was set.

This made setting the intended space-type run the 3D views exit callback
on a 3D view without a View3D struct allocated, which the exit callback
needed to account for.

Resolve by calling ED_screen_change after the area type has been set.