Diffusion - maybe fix import spam bug

Summary: Ref T6350. I just set up a repository to import secure.phabricator.com/P and saw an error in my error logs about this, creating a fatal around when we publish feed stories. this is late enough in the editor code path I could see it firing again and again and again...

Test Plan: the first phabricator commit ever only had one duplicated transaction before i applied this patch. its yet to do it again. otherwise, ask some users with the issue to deploy it and see if it fixes things for them too.

Reviewers: epriestley, chad

Reviewed By: chad

Subscribers: Korvin, epriestley

Maniphest Tasks: T6350

Differential Revision: https://secure.phabricator.com/D10729

Author: bobtrahan

src/applications/feed/PhabricatorFeedStoryPublisher.php

@@ -121,8 +121,8 @@ public function publish() {
     }
 
     $subscribed_phids = $this->subscribedPHIDs;
-    $subscribed_phids = $this->filterSubscribedPHIDs($subscribed_phids);
     if ($subscribed_phids) {
+      $subscribed_phids = $this->filterSubscribedPHIDs($subscribed_phids);
       $this->insertNotifications($chrono_key, $subscribed_phids);
       $this->sendNotification($chrono_key, $subscribed_phids);
     }