array type throwing error

This fixes the following error (after update from 2.3.3RC1 to 2.4RC1)

```
Symphony Warning: array_key_exists() expects parameter 2 to be array, null given
An error occurred in /var/www/oliberal/symphony/lib/core/class.administration.php around line 237
```
```
232                             else {
233                                 throw $ex;
234                             }
235                         }
236
237                         if(array_key_exists('status', $about) && in_array(EXTENSION_REQUIRES_UPDATE, $about['status'])) {
238                             $this->Page->pageAlert(
239                                 __('An extension requires updating.') . ' <a href="' . SYMPHONY_URL . '/system/extensions/">' . __('View extensions') . '</a>'
240                             );
241                             break;
```