Fix redirects in Phragment

Summary: This fixes the ZIP controller redirect in Phragment after the external redirect change.

Test Plan: Tested it on my server.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: epriestley, Korvin, hach-que

Differential Revision: https://secure.phabricator.com/D10350

src/applications/phragment/controller/PhragmentZIPController.php

@@ -123,6 +123,7 @@ final class PhragmentZIPController extends PhragmentController {
     }
 
     return id(new AphrontRedirectResponse())
+      ->setIsExternal(true)
       ->setURI($file->getDownloadURI($return));
   }