Default to right status when viewing a config 'class' option

Summary: T2361

Test Plan:
Set value to metamta.mail-adapter and reload page.  Defaults to assigned value.
Performed same test with metamta.can-send-as-user to check that functionality is not broken for config 'boolean' options.

Reviewers: epriestley

Reviewed By: epriestley

CC: kwadwon, aran, Korvin

Maniphest Tasks: T2361

Differential Revision: https://secure.phabricator.com/D4881

src/applications/config/controller/PhabricatorConfigEditController.php

@@ -330,6 +330,7 @@ final class PhabricatorConfigEditController
       case 'int':
       case 'string':
       case 'enum':
+      case 'class':
         return $value;
       case 'bool':
         return $value ? 'true' : 'false';