Fix of issue with different url types

Hmm...this seems broken. Shouldn't it be...
return $this->callback_url . (strpos($this->callback_url, '?') == false ? '?' : '&') . 'order=' . $order_id;
or even better (I don't like the implicit typing of ints and booleans in the line above)...
return $this->callback_url . (array_key_exists('query',parse_url($this->callback_url)) ? '&' : '?') . 'order=' . $order_id;