Prevent double lightbox in lightbox comments

Summary: Ref T3612, prevents lightbox from spawning from inside a lightbox.

Test Plan: Click on file lightbox, leave file comment, click file comment, get take to file page instead of another lightbox.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Maniphest Tasks: T3612

Differential Revision: https://secure.phabricator.com/D16978

src/view/page/PhabricatorStandardPageView.php

@@ -512,6 +512,7 @@ final class PhabricatorStandardPageView extends PhabricatorBarePageView
       'div',
       array(
         'class' => implode(' ', $classes),
+        'id' => 'main-page-frame',
       ),
       array(
         $main_page,