This was introduced in 6c9ec1c893. The overlays can now be drawn when
PBVH drawing is not enabled, but the PBVH should still exist in the
SculptSession in order to draw them. Before, it was avoiding the crash
by checking use_pbvh as BKE_sculptsession_use_pbvh_draw also checks if
the PBVH exists.
Reviewed By: sergey
Maniphest Tasks: T81268
Differential Revision: https://developer.blender.org/D9044