Conpherence - fix a bug where users have no events

Summary: Fixes T8518. Defaulting $events to null creates carnage further down the stack. Instead, default it to array() so foreach, array_select_keys, etc. don't barf.

Test Plan: logic and will ask the reporting user to verify since they can repro 100%

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: epriestley, Korvin

Maniphest Tasks: T8518

Differential Revision: https://secure.phabricator.com/D13314

src/applications/conpherence/query/ConpherenceThreadQuery.php

@@ -355,6 +355,7 @@ final class ConpherenceThreadQuery
     $start_epoch = $epochs['start_epoch'];
     $end_epoch = $epochs['end_epoch'];
 
+    $events = array();
     if ($participant_phids) {
       $events = id(new PhabricatorCalendarEventQuery())
         ->setViewer($this->getViewer())
@@ -363,8 +364,6 @@ final class ConpherenceThreadQuery
         ->withDateRange($start_epoch, $end_epoch)
         ->execute();
       $events = mpull($events, null, 'getPHID');
-    } else {
-      $events = null;
     }
 
     $invitees = array();