This crash occurs when the bone is newly created. In certain
circumstances the depsgraph data for the armature is not updated,
causing `pchan_eval` to be NULL when the parent is updated. This causes
a segfault in `ED_object_parent_set` when the flags are updated.
This change fixes the underlying depsgraph bug, and also adds both an
assertion and NULL pointer check to `ED_object_parent_set` to better
handle this scenario if it recurs via another path.
Maniphest Tasks: T94441
Differential Revision: https://developer.blender.org/D16065
4bdba62cb9