fixes CNVS-9879
This is tricky to test, since ZachP already fixed the bug.
See https://gerrit.instructure.com/#/c/26059/ .
Consider manually breaking your own data:
UPDATE conversation_participants SET last_message_at = NOW() WHERE message_count = 0;
Change-Id: Id8eb4c23ff2968f7ab4ec6856629f76b82cb9515
Reviewed-on: https://gerrit.instructure.com/27121
Reviewed-by: Jacob Fugal <jacob@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Steven Shepherd <sshepherd@instructure.com>
Product-Review: Braden Anderson <banderson@instructure.com>
Braden Anderson