Fix Differential flag view bug
Summary: See D3125#3
Test Plan:
Well, apparently the FB test Phabricator has no other flags
in it, so I modified the database by hand... the changed revision was
not marked as flagged in Differential.
Reviewers: epriestley
Reviewed By: epriestley
CC: aran, Korvin
Maniphest Tasks: T1557
Differential Revision: https://secure.phabricator.com/D3130