Fix an issue with FileMailReceiver not working well

Summary: Ref T7199. Guess no one has ever tried to reply to file mail.

Test Plan: Used `bin/mail receive-test` to send mail to files.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T7199

Differential Revision: https://secure.phabricator.com/D12228

src/applications/files/mail/FileMailReceiver.php

@@ -14,7 +14,7 @@ final class FileMailReceiver extends PhabricatorObjectMailReceiver {
   protected function loadObject($pattern, PhabricatorUser $viewer) {
     $id = (int)trim($pattern, 'F');
 
-    return id(new PhabricatorPasteQuery())
+    return id(new PhabricatorFileQuery())
       ->setViewer($viewer)
       ->withIDs(array($id))
       ->executeOne();