Blender Git Loki

Fix [#36530] Texture tab refreshing problem

That was not really a bug (code working as expected), but the way tex context was handled was a bit raw, now it is much smarter:
* Default fallback context (when current one is no more valid) will now choose "most specific" ones first (i.e. material/lamp/particules before world and "others").
* When using that default fallback context, previous one is stored and we try to revive it later, if possible. Thus e.g. object[mat tex ctxt] -> empty[default world ctxt] -> object[mat tex ctxt] is now working as expected.
* However, when user explicitely or implicitely (through e.g. going to Material context...) sets a tex context, previous one is not stored, so that only default fallback context switch may later automatically revive a previous (presumably user-set) context.