This is a temp fix for a better system.
Currently the studiolights can be referenced by a WM_job and being freed
via the API. This can happen when removing a studiolight via the
interface.
As the studiolight has no relation with the job, it is hard to detect if
it is still being used. I tried with a Mutex and a Thread Queue but they
were failing.
So the current temp fix is to keep the studiolights in memory until you
close blender. This Must be fixed ASAP! I added this fix so normal cases
can workish.
0116c95d4c