Fix fatal when looking at an unknown-config error.
Summary:
Going to /config/issue/config.unknown.phabricator.setup/ fataled with
Call to a member function getLocked() on a non-object
Test Plan: Went to /config/issue/config.unknown.phabricator.setup/ and saw the page render.
Reviewers: epriestley, btrahan
Reviewed By: epriestley
CC: aran, Korvin
Differential Revision: https://secure.phabricator.com/D4633