Silence coverity (CID 1465243)
Silence coverity (CID 1465243)

Check the return value of repo_get_remote_collection_id like we do
in other places. This doesn't really affect the result, because
we return NULL both before and after in the failure case, but
it makes things clearer.

matthiasclasen/flatpak,handsome-feng/flatpak,handsome-feng/flatpak,flatpak/flatpak,matthiasclasen/flatpak,handsome-feng/flatpak,matthiasclasen/flatpak,flatpak/flatpak,flatpak/flatpak,flatpak/flatpak,matthiasclasen/flatpak,matthiasclasen/flatpak,flatpak/flatpak,handsome-feng/flatpak,handsome-feng/flatpak