Policy - lock down file loading in mail reply handler path

Summary: Ref T7094. This one is really straight-forward since $this->actor is always populated and the right thing to do here.

Test Plan: used the ole thinking noodle since testing email w/ attachments is really hard

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T7094

Differential Revision: https://secure.phabricator.com/D11589

src/applications/metamta/replyhandler/PhabricatorMailReplyHandler.php

@@ -325,9 +325,10 @@ abstract class PhabricatorMailReplyHandler {
       return $body;
     }
 
-    // TODO: (T603) What's the policy here?
+    $files = id(new PhabricatorFileQuery())
-    $files = id(new PhabricatorFile())
+      ->setViewer($this->getActor())
-      ->loadAllWhere('phid in (%Ls)', $attachments);
+      ->withPHIDs($attachments)
+      ->execute();
 
     // if we have some text then double return before adding our file list
     if ($body) {