Fix three minor edge case behaviors in Conpherence
Summary:
Couple of tweaks:
- If a conpherence has no participants, we fail to `attachParticipants()`. This can happen if you leave a Conpherence as the last participant, then visit the URI again explicitly.
- If you can't load any transactions (usually, because you don't have permission to view a thread's transactions), we try to attach `null` instead of `array()`. This can happen if you attempt to view a thread you don't have permission to see. A more general fix would be to tweak the load/filtering order, but I'm leaving that for another time since it's more involved and only gives us a small performance gain in unusual sitautions.
- `initializeNewThread()` should be declared `static`.
Test Plan:
- Viewed a thread with no participants, got proper policy error.
- Viewed a thread I couldn't see, got proper policy error.
- Grepped for `initializeNewThread()`.
Reviewers: btrahan
Reviewed By: btrahan
CC: aran
Differential Revision: https://secure.phabricator.com/D8467