Fix bad Phortune Subscriptions query
Fixes T7285. If the user tries to view a subscription they don't have permission to view, we may filter all the subscriptions out, then still try to load related data. This can fatal because it's invalid.
Instead, bail if we filtered everything.
Test Plan: Subscritption detail page of another user's subscription is now 404 instead of fatal.
Reviewers: btrahan, chad
Reviewed By: chad
Maniphest Tasks: T7285
Differential Revision: https://secure.phabricator.com/D11780