FEM: vtk mesh builder, fix crash if SMESH grid has node gaps
FEM: vtk mesh builder, fix crash if SMESH grid has node gaps

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