services_dyndns_edit: wrong parameter type for htmlspecialchars, closes...

services_dyndns_edit: wrong parameter type for htmlspecialchars, closes https://github.com/opnsense/core/issues/813

(cherry picked from commit 9da1b92e)

src/www/services_dyndns_edit.php

@@ -261,7 +261,7 @@ include("head.inc");
                         $iflist = array_merge($iflist, return_gateway_groups_array());
                         foreach ($iflist as $if => $ifdesc):?>
                           <option value="<?=$if;?>" <?=$pconfig['interface'] == $if ? "selected=\"selected\"" : "";?>>
-                            <?=htmlspecialchars($ifdesc);?>
+                            <?=is_array($ifdesc) ? $if : htmlspecialchars($ifdesc);?>
                           </option>
 
 <?php
@@ -278,7 +278,7 @@ include("head.inc");
                        $iflist = array_merge($iflist, return_gateway_groups_array());
                        foreach ($iflist as $if => $ifdesc):?>
                          <option value="<?=$if;?>" <?=$pconfig['requestif'] == $if ? "selected=\"selected\"" : "";?>>
-                           <?=htmlspecialchars($ifdesc);?>
+                           <?=is_array($ifdesc) ? $if : htmlspecialchars($ifdesc);?>
                          </option>
 
 <?php