Don't apply space constraints to omnipotent-viewer queries

Summary:
Fixes T8743. Fixes T8746. When running queries with the omnipotent viewer and no explicit space constraints, don't add implicit space constraints.

This prevents us from fataling when running older pre-space migrations and trying to load space-aware objects.

Test Plan: Manually ran migrations with --trace, verified no WHERE spacePHID = ....

Reviewers: btrahan, chad

Reviewed By: chad

Subscribers: eadler, epriestley

Maniphest Tasks: T8743, T8746

Differential Revision: https://secure.phabricator.com/D13542