Blender Git Loki

Fix (unreported) Separate bones creates empty armature

Fix for fix (rB8bf7ca9fe31c).
The fix was not actually working [neither for multi-armature-editing as
intended nor for single armatures] and it broke single-armature bone
separation completely.

More or less indentation issue, move relevant code out of bone loop, do
after all bones have been checked, guess this was intended anyways.

Differential Revision: https://developer.blender.org/D6949