core: Prevent crash on missing element
core: Prevent crash on missing element

GNOME/rygel,Pelagicore/Media-Manager-Rygel-patched,jku/rygel,Tarnyko/rygel,GNOME/rygel,Pelagicore/Media-Manager-Rygel-patched,jku/rygel,Tarnyko/rygel,GNOME/rygel,Pelagicore/Media-Manager-Rygel-patched