Fix external blog images

Summary: Reading the code, this seems correct, but I don't have a local test. Ref T9897

Test Plan: read carefully

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Maniphest Tasks: T9897

Differential Revision: https://secure.phabricator.com/D16148

src/applications/phame/site/PhameBlogSite.php

@@ -39,6 +39,7 @@ final class PhameBlogSite extends PhameSite {
         ->setViewer(new PhabricatorUser())
         ->withDomain($host)
         ->needProfileImage(true)
+        ->needHeaderImage(true)
         ->withStatuses(
           array(
             PhameBlog::STATUS_ACTIVE,