fetcher: Unref pending result when completing
fetcher: Unref pending result when completing

Otherwise we were just leaking it.

https://bugzilla.gnome.org/show_bug.cgi?id=725921

gatispaeglis/ostree,sujitfulse/ostree,gatispaeglis/ostree,GNOME/ostree,leandrosansilva/ostree,resin-io/ostree,leandrosansilva/ostree,GNOME/ostree,gatispaeglis/ostree,resin-io/ostree,leandrosansilva/ostree,leandrosansilva/ostree,GNOME/ostree,GNOME/ostree,gatispaeglis/ostree,sujitfulse/ostree,resin-io/ostree,leandrosansilva/ostree,gatispaeglis/ostree,resin-io/ostree,GNOME/ostree,sujitfulse/ostree,sujitfulse/ostree,sujitfulse/ostree,gatispaeglis/ostree,resin-io/ostree