1148937 - Repo group publish fails when there are no repo members in the group


Since there were no repo-members in the repo group, publish could not proceed
because there were not present listing file and realized directory.
find_by_id_list() retuns a generator of dict wchich is stored in  `repos`. not sure if it is possible to check the generator for emptiness, at least I did not find any better solution then introducing the `empty_repos` check.