Fix issue where folder selector wasn't visible on new filter form

plugins/managesieve/Changelog

@@ -1,5 +1,6 @@
 - Nicely handle server-side modification of script names (#1489412)
 - Add Filters tab/section using plugin API hook
+- Fix issue where folder selector wasn't visible on new filter form
 
 * version 7.1 [2013-11-22]
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plugins/managesieve/lib/Roundcube/rcube_sieve_engine.php

@@ -1788,7 +1788,7 @@ class rcube_sieve_engine
             'maxlength' => 100,
             'id' => 'action_mailbox' . $id,
             'name' => "_action_mailbox[$id]",
-            'style' => 'display:'.(!isset($action) || $action['type']=='fileinto' ? 'inline' : 'none')
+            'style' => 'display:'.(empty($action['type']) || $action['type'] == 'fileinto' ? 'inline' : 'none')
         ));
         $out .= $select->show($mailbox);
         $out .= '</td>';