Improved request error handling.

src/Microsoft.AspNetCore.Server.WebListener/MessagePump.cs

@@ -127,7 +127,7 @@ namespace Microsoft.AspNetCore.Server.WebListener
                     {
                         LogHelper.LogException(_logger, "ListenForNextRequestAsync", exception);
                     }
-                    return;
+                    continue;
                 }
                 try
                 {

src/Microsoft.Net.Http.Server/AsyncAcceptContext.cs

@@ -79,6 +79,11 @@ namespace Microsoft.Net.Http.Server
                                 complete = true;
                             }
                         }
+                        catch (Exception)
+                        {
+                            server.SendError(asyncResult._nativeRequestContext.RequestId, HttpStatusCode.BadRequest);
+                            throw;
+                        }
                         finally
                         {
                             if (stoleBlob)

src/Microsoft.Net.Http.Server/WebListener.cs

@@ -318,7 +318,7 @@ namespace Microsoft.Net.Http.Server
             return true;
         }
 
-        private unsafe void SendError(ulong requestId, HttpStatusCode httpStatusCode, IList<string> authChallenges)
+        internal unsafe void SendError(ulong requestId, HttpStatusCode httpStatusCode, IList<string> authChallenges = null)
         {
             HttpApi.HTTP_RESPONSE_V2 httpResponse = new HttpApi.HTTP_RESPONSE_V2();
             httpResponse.Response_V1.Version = new HttpApi.HTTP_VERSION();