gistfile1.txt

// Rewrite
- if ($shippingInfo && $shippingInfo['cost'] && $this->formatPrice($shippingInfo['cost'] != 0)) {
+ if (isset($shippingInfo['cost']) && $this->formatPrice($shippingInfo['cost']) > 0)

- $order_id = $this->request->get['order_id'];
+ $order_id = (int) $this->request->get['order_id'];

// Refactor
private function formatPrice($number)
{
    return round((float) $number, 2);
}

private function getShippingInfo()
{
    return isset($this->session->data['shipping_method'])
        ? (array) $this->session->data['shipping_method']
        : null;
}

private function getSiteUrl()
{
    return self::isHttps()
        ? ($this->config->get('config_ssl') ?: HTTPS_SERVER)
        : ($this->config->get('config_url') ?: HTTP_SERVER);
}

private function getServerConnectionSlug()
{
    return self::isHttps() ? 'SSL' : 'NONSSL';
}

private static function isHttps()
{
    static $ret;

    isset($ret) || $ret =@ (
        $_SERVER['REQUEST_SCHEME'] == 'https' ||
        $_SERVER['SERVER_PORT']    == '443'   ||
        $_SERVER['HTTPS']          == 'on'
    );

    return $ret;
}