R1:671986592baf

Add a missing "GROUP BY" to MailQuery when querying for multiple recipients

Summary:
See <https://discourse.phabricator-community.org/t/mail-details-view-broken/4315>. The change in D21400 detects a missing "GROUP BY" in some variations of this query.

Specifically, we may join multiple recipient rows (since mail may have multiple recipients) and then fail to group the results.

Fix this by adding the "GROUP BY". Additionally, remove the special-cased behavior when no authors or recipients are specified…