Fix SendAsync in HttpUtils to only run on success

Author: mythz

src/ServiceStack.Text/HttpUtils.cs

@@ -353,15 +353,15 @@ public static Task<string> SendStringToUrlAsync(this string url, string method =
                 var webRes = task.Result;
                 if (responseFilter != null)
                 {
-                    responseFilter((HttpWebResponse)webRes);
+                    responseFilter(webRes);
                 }
 
                 using (var stream = webRes.GetResponseStream())
                 using (var reader = new StreamReader(stream))
                 {
                     return reader.ReadToEnd();
                 }
-            });
+            }, TaskContinuationOptions.NotOnFaulted | TaskContinuationOptions.OnlyOnRanToCompletion);
         }
 
         public static string SendStringToUrl(this string url, string method = null,