make sort controls only show up if sorting will work

Summary: T2326 tells the tale. this is the fix.

Test Plan: verified that queries that shouldn't be sortable weren't. also had a phlog in there a bit to sanity check things faster

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T2326

Differential Revision: https://secure.phabricator.com/D4816

src/applications/maniphest/controller/ManiphestTaskListController.php

@@ -330,8 +330,8 @@ final class ManiphestTaskListController extends ManiphestController {
       $group = $query->getParameter('group');
       $order = $query->getParameter('order');
       $is_draggable =
-        ($group == 'priority') ||
-        ($group == 'none' && $order == 'priority');
+        ($order == 'priority') &&
+        ($group == 'none' || $group == 'priority');
 
       $lists = new AphrontNullView();
       $lists->appendChild('<div class="maniphest-group-container">');