Fix some exception handling (#5704)

Preserves the original stacktrace when AsyncResult is throwing stored exception

Fix order of null checks so that SocketConnection actually throws stored exception when failing to connect

Author: mconnew

src/System.ServiceModel.NetTcp/src/System/ServiceModel/Channels/SocketConnection.cs

@@ -969,17 +969,17 @@ public async ValueTask<IConnection> ConnectAsync(Uri uri, TimeSpan timeout)
                 }
             }
 
-            if (socketConnection == null)
+            if (lastException != null)
             {
                 throw DiagnosticUtility.ExceptionUtility.ThrowHelperError(
-                    new EndpointNotFoundException(SR.Format(SR.NoIPEndpointsFoundForHost, uri.Host)));
+                    SocketConnectionInitiator.ConvertConnectException(lastException, uri,
+                    timeoutHelper.ElapsedTime(), lastException));
             }
 
-            if (lastException != null)
+            if (socketConnection == null)
             {
                 throw DiagnosticUtility.ExceptionUtility.ThrowHelperError(
-                    SocketConnectionInitiator.ConvertConnectException(lastException, uri,
-                    timeoutHelper.ElapsedTime(), lastException));
+                    new EndpointNotFoundException(SR.Format(SR.NoIPEndpointsFoundForHost, uri.Host)));
             }
 
             return socketConnection;

src/System.ServiceModel.Primitives/src/Internals/System/Runtime/AsyncResult.cs

@@ -3,6 +3,7 @@
 // See the LICENSE file in the project root for more information.
 
 
+using System.Runtime.ExceptionServices;
 using System.Threading;
 
 namespace System.Runtime
@@ -348,7 +349,7 @@ protected static TAsyncResult End<TAsyncResult>(IAsyncResult result)
 
             if (asyncResult._exception != null)
             {
-                throw Fx.Exception.AsError(asyncResult._exception);
+                ExceptionDispatchInfo.Capture(Fx.Exception.AsError(asyncResult._exception)).Throw();
             }
 
             return asyncResult;