Change how `action_foreach_id()` reports action slot users. This contains
two changes:
- Report the correct pointer reference, so that the ID remapping code
can actually change the pointers in the cache (necessary, for example,
to nil pointers to deleted IDs).
- Never report anything when it's known the slot user cache is dirty.
Pull Request: https://projects.blender.org/blender/blender/pulls/131808
de6c65b347