core: Throw more specific error
core: Throw more specific error

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