Fix of a crash when deleting an object while it is edited with the smooth variable layer editing tool.
Fix of a crash when deleting an object while it is edited
with the smooth variable layer editing tool.

prusa3d/Slic3r,prusa3d/Slic3r,prusa3d/Slic3r,prusa3d/Slic3r,prusa3d/Slic3r,prusa3d/Slic3r,prusa3d/Slic3r