/api/v4/:project_id/languages returning 500 for archived projects

Problem to solve

Offer consistent responses

Further details

If the project is archived, querying for the language of the project results in a HTTP500 response, which always have to be treated. If there is no way to get the languages from an archived repo (maybe it should be possible?) at least I'd prefer an empty result.

Proposal

Return an empty result with HTTP200 status code