Fix exception when viewing Owners packages owned by projects you are a member of

Summary: Fixes T3188. See that task for details.

Test Plan: Viewed packages with and without project membership; no more exception.

Reviewers: btrahan, chad

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T3188

Differential Revision: https://secure.phabricator.com/D5918