Bastien Montagne
5949d598bc
There are cases where there is no way to ensure we do have/know about an active scene. Further more, this should not be required to perform 'real' updates on data, only to perform additional special handling in current scene (mostly related to editing tools, UI, etc.). This pointer is actually almost never used in practice, and half of its current usages are fairly close to abuse of the system (like calls to `ED_gpencil_tag_scene_gpencil` or `BKE_rigidbody_cache_reset`). This commit ensures that the few places using this 'active scene' pointer are safely handling the `NULL` case, and clearly document the fact that a NULL scene pointer is valid.