Fix issue with empty data for some filter-selections on the Repositories page

Only those repositories / publishers should be listed in the dropdown menu on the "Repositories" page, for which data linked as "issupplementedby" to literature is found.

Otherwise the user will select some of them and see the error message "no data was found".

In the version where multiple publishers are allowed, this is currently not yet fully implemented. Please review and potentially fix this issue.