HttpWebResponse: игнорировать ошибки

string result = string.Empty;
            string pattern = "Duplicate entry '(.*):1' for key 'group_key'";
            string postData = "query=x35a2fv&titleonly=0&searchuser=&exactname=1&tag=&dosearch=%CD%E0%F7%E0%F2%FC+%EF%EE%E8%F1%EA&searchdate=0&beforeafter=after&sortby=relevance&order=descending&humanverify%5Binput%5D=11&humanverify%5Bhash%5D=f8b17252abed95a712d692000a928a77&s=&securitytoken=guest&do=process&searchthreadid=1";
            HttpWebRequest req = (HttpWebRequest)WebRequest.Create(url + "search.php?do=process");
            req.UserAgent = "Mozilla/5.0 (Windows NT 5.1; rv:13.0) Gecko/20100101 Firefox/13.0.1";
            req.Method = "POST";
            req.AllowAutoRedirect = true;
            req.ContentType = "application/x-www-form-urlencoded";
            byte[] encodedData = Encoding.ASCII.GetBytes(postData);
            req.ContentLength = encodedData.Length;
            req.GetRequestStream().Write(encodedData, 0, encodedData.Length);
            req.GetRequestStream().Close();
 
            HttpWebResponse resp = (HttpWebResponse)req.GetResponse();
            string html = new StreamReader(resp.GetResponseStream(), Encoding.GetEncoding(1251)).ReadToEnd();
            Match res;
            res = Regex.Match(html, pattern);
            result = res.Groups[1].ToString();
            return result;

try
{
    HttpWebResponse resp = (HttpWebResponse)req.GetResponse();
}
catch
{
    return;
}