Fix not blocking / not blocked queries
Summary: Fixes T7434. We need to LEFT JOIN, not JOIN here, because we still want result rows where the value is null.
Test Plan: Issued blocked/not-blocked + blocking/not-blocking queries, got results in all cases.
Reviewers: btrahan
Reviewed By: btrahan
Subscribers: epriestley
Maniphest Tasks: T7434
Differential Revision: https://secure.phabricator.com/D11939