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

src/applications/conpherence/query/ConpherenceThreadQuery.php

@@ -129,12 +129,20 @@ final class ConpherenceThreadQuery
     $participants = id(new ConpherenceParticipant())
       ->loadAllWhere('conpherencePHID IN (%Ls)', array_keys($conpherences));
     $map = mgroup($participants, 'getConpherencePHID');
-    foreach ($map as $conpherence_phid => $conpherence_participants) {
-      $current_conpherence = $conpherences[$conpherence_phid];
+
+    foreach ($conpherences as $current_conpherence) {
+      $conpherence_phid = $current_conpherence->getPHID();
+
+      $conpherence_participants = idx(
+        $map,
+        $conpherence_phid,
+        array());
+
       $conpherence_participants = mpull(
         $conpherence_participants,
         null,
         'getParticipantPHID');
+
       $current_conpherence->attachParticipants($conpherence_participants);
       $current_conpherence->attachHandles(array());
     }
@@ -183,13 +191,13 @@ final class ConpherenceThreadQuery
     $transactions = $query->execute();
     $transactions = mgroup($transactions, 'getObjectPHID');
     foreach ($conpherences as $phid => $conpherence) {
-      $current_transactions = $transactions[$phid];
+      $current_transactions = idx($transactions, $phid, array());
       $handles = array();
       foreach ($current_transactions as $transaction) {
         $handles += $transaction->getHandles();
       }
       $conpherence->attachHandles($conpherence->getHandles() + $handles);
-      $conpherence->attachTransactions($transactions[$phid]);
+      $conpherence->attachTransactions($current_transactions);
     }
     return $this;
   }

src/applications/conpherence/storage/ConpherenceThread.php

@@ -18,7 +18,7 @@ final class ConpherenceThread extends ConpherenceDAO
   private $widgetData = self::ATTACHABLE;
   private $images = array();
 
-  public function initializeNewThread(PhabricatorUser $sender) {
+  public static function initializeNewThread(PhabricatorUser $sender) {
     return id(new ConpherenceThread())
       ->setMessageCount(0)
       ->setTitle('');