Fixed Issue #3830 mdbox format not working in mailboxes.

Till Brehm

2016-04-20 ef6e5d764118bcc2918be9cfd7b76c31b24a1eb4

 interface/lib/classes/listform.inc.php

@@ -563,7 +563,7 @@
               break;

            case 'DATE':
               if($record[$key] != '' && $record[$key] != '0000-00-00') {
               if($record[$key] != '' && !is_null($record[$key]) && $record[$key] != '0000-00-00') {
                  $record[$key] = $record[$key];
               }
               break;