Fix of #4060 - Add check for the case that all ranges of a volume do not contain any Z.
Fix of #4060 - Add check for the case that all ranges of a volume do not contain any Z.

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