fix crash in SymbolChooser in case it's empty and Ok is clicked
fix crash in SymbolChooser in case it's empty and Ok is clicked

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