Issue #2682
Issue #2682

Modifying a check in SketchObject::validateExternalLinks() for datums.
Hopefully will not cause trouble.
There is still a problem where if the check fails, all constraints will
be lost!

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