Fixes T13345. See D20650. Currently, PhabricatorCursorPagedPolicyAwareQuery does a JOIN against the "title" field so it can apply additional ranking/ordering conditions to the query.
This means that documents with no title (which don't have this field) are always excluded from the result set.
We'd prefer to include them, just not give them any bonus ranking/relevance boost. Use a LEFT JOIN so they get included.