When trying to select bones that are inside other bones which are not selectable,
the selection would fail. This is inconsistent with object mode, where unselectable
things are just ignored.
This patch fixes it for pose mode and edit mode.
Note that there are two areas for edit mode that were modified.
The one in `ed_armature_pick_bone_from_selectbuffer/202` is never actually reached,
but I added the code there for completeness.
The code in `get_nearest_editbonepoint` had to be modified some more to
implement a similar logic as `armature_select.cc/220`
Pull Request: https://projects.blender.org/blender/blender/pulls/129120
328ec2b172