Add slash to image urls

Apparently not doing this is technically invalid

classes/imagetools.class.php

     if (preg_match('/^https:\/\/('.SITE_DOMAIN.'|'.IMAGE_DOMAIN.')\//', $Url) || $Url[0]=='/') {
       return $Url;
     } else {
-      return 'https://'.IMAGE_DOMAIN.'?h='.rawurlencode(base64_encode(hash_hmac('sha256', $Url, IMAGE_PSK, true))).'&i='.urlencode($Url);
+      return 'https://'.IMAGE_DOMAIN.'/?h='.rawurlencode(base64_encode(hash_hmac('sha256', $Url, IMAGE_PSK, true))).'&i='.urlencode($Url);
     }
   }