Blender Git Loki

fix/disallow [#26502] segmentationfault on pressing button to browse existing images for UV window

creating RNA within draw functions can free existing RNA, crashing blender when this is already used in the UI.
disallowing this so it raises a python exception.

This was being used to dynamically generate addon categories so for now they are hard coded and we need proper enum-functions for python to do this.