FEM: vtk tools, fix crash in mesh builder if not supported volume is used
FEM: vtk tools, fix crash in mesh builder if not supported volume is used

Fat-Zer/FreeCAD_sf_master,Fat-Zer/FreeCAD_sf_master,Fat-Zer/FreeCAD_sf_master,Fat-Zer/FreeCAD_sf_master,Fat-Zer/FreeCAD_sf_master