Clean up ProjectQuery when viewer is logged-out or omnipotent

Summary:
Ref T10010. When the viewer is logged-out or omnipotent, we can skip this query.

(Currently we issue a silly query like src = X AND type = Y AND dst = '', which will never return results.)

Test Plan:

• Viewed projects as normal user and logged-out user.
• Ran unit tests.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10010

Differential Revision: https://secure.phabricator.com/D14892