R1:042ab0ad9d03

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…