Always allow users to access their own review requests.

In cases where a user assigned a review request to a private group of which they
were not a member, they'd lose access to their own request. This was pretty bad.
I've added an explicit check for ownership to ensure that users always have
access to their own review requests.

Created a review as a non-admin user and assigned it to a private review group.
Saw that I could no longer access it. Applied this change and reloaded, and saw
that I could see it again. New unit test fails before the change and succeeds
after.