In the event that a unified view has a comment thread group with threads
on either side for comments posted on the same line, fetching a thread
group may incorrectly match a thread for the wrong side, when it really
needs to either find another existing one or create a new one.
This is fixed by also filtering comment threads by side in addition to
range.
Change-Id: Ia4568ea71ca954e74d8bbf8dbc97251b996ef6a2