Disable OpenMP with dyntopo in paint_mesh_restore_co()

Otherwise, new entries might be inserted by sculpt_undo_push_node()
into the GHash used internally by BM_log_original_vert_co() by a
different thread.

Fixes bug [#33787]
http://projects.blender.org/tracker/?func=detail&aid=33787&group_id=9&atid=498

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@53913 954f8c5b-7b00-dc11-b283-0030488c597c