When rendering the "you were invited" header, query the inviting user with the omnipotent viewer
Summary: Fixes T11982. If an install is not public, the registering user may not be able to see the inviting user.
Test Plan:
Reviewers: chad
Reviewed By: chad
Maniphest Tasks: T11982
Differential Revision: https://secure.phabricator.com/D17015