Blender Git Loki

Fix Pose Brush crashing after disabling connected only in FK mode

This function was returning the ik_chain before disabling the
fake_neighbors, so when the brush was used again with fake neighbors
disabled after rebuilding the PBVH and free them, they were still
enabled in the SculptSession, causing a the crash.

Reviewed By: sergey

Differential Revision: https://developer.blender.org/D8195