fixes #0002926: Trying to access Part.Shape.children() before doc.recompute() crashes the whole program
fixes #0002926: Trying to access Part.Shape.children() before doc.recompute() crashes the whole program

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