R1:787c59744be8

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