Improve behavior for not-yet-created non-cluster repositories

Summary: Fixes T10815. We already recovered reasonably from this for cluster repositories, but not for non-cluster repositories.

Test Plan:

• Viewed cluster and non-cluster empty Git repository.
• Viewed cluster and non-cluster empty Mercurial repository.
• Viewed cluster and non-clsuter empty hosted SVN repository.
• Viewed cluster and non-cluster empty observed SVN repository.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10815

Differential Revision: https://secure.phabricator.com/D15878