Correctly attach users to identities
Summary: This never worked.
Test Plan: Ran `bin/repository rebuild-identities` and viewed identity objects with `currentEffectiveUserID`s and no longer got errors about attempting to attach `null` objects instead of `PhabricatorUser` objects.
Reviewers: epriestley
Reviewed By: epriestley
Subscribers: Korvin
Differential Revision: https://secure.phabricator.com/D19495