Prevent notice for missing configuration in PhabricatorIRCDifferentialNotificationHandler

Summary: Provide array() default so we don't foreach() over null in the case of a missing config (from @dctrwatson).

Test Plan: Will verify with @dctrwatson.

Reviewers: vrana, btrahan, dctrwatson

Reviewed By: vrana

CC: aran

Differential Revision: https://secure.phabricator.com/D3686

src/infrastructure/daemon/irc/handler/PhabricatorIRCDifferentialNotificationHandler.php

@@ -57,7 +57,8 @@ final class PhabricatorIRCDifferentialNotificationHandler
       $actor_name = $handles[$actor_phid]->getName();
       $message = "{$actor_name} {$verb} revision D".$data['revision_id'].".";
 
-      foreach ($this->getConfig('notification.channels') as $channel) {
+      $channels = $this->getConfig('notification.channels', array());
+      foreach ($channels as $channel) {
         $this->write('PRIVMSG', "{$channel} :{$message}");
       }
     }