core: Only query parent once
core: Only query parent once

The parent node was queried for each child which was totally useless.
Code now at least twice as fast

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