fixes 0003894: Part Thickness dialog thickness field not Expressions enabled
fixes 0003894: Part Thickness dialog thickness field not Expressions enabled

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