It's possible for the `bArmature.collection_array` to be null if Bone
Collections were never added after armature creation. This could trip up
undo processing later when we call `MEM_freeN` on the collection.
Use a `MEM_SAFE_FREE` call instead which handles checking for null, as
well as setting to null when complete.
Pull Request: https://projects.blender.org/blender/blender/pulls/126945
787eb2b433