R1:5f615c1e6e17

Fix a warning when viewing a revision not attached to a repository

Summary: We'll get a typehint warning on the repository if there's no repository. Check outside the method instead.

Test Plan: Loaded page, no warning.

Reviewers: btrahan, vrana, jungejason

Reviewed By: vrana

CC: aran

Differential Revision: https://secure.phabricator.com/D2194