Avoid crash when tunnel cannot be opened

When client.Tunnel() returns an error, then the returned
stream is invalid and must not be used.

Signed-off-by: Jan Dubois <jan.dubois@suse.com>

pkg/portfwd/client.go

@@ -21,6 +21,7 @@ func HandleTCPConnection(ctx context.Context, client *guestagentclient.GuestAgen
 	stream, err := client.Tunnel(ctx)
 	if err != nil {
 		logrus.Errorf("could not open tcp tunnel for id: %s error:%v", id, err)
+		return
 	}
 
 	g, _ := errgroup.WithContext(ctx)
@@ -54,6 +55,7 @@ func HandleUDPConnection(ctx context.Context, client *guestagentclient.GuestAgen
 	stream, err := client.Tunnel(ctx)
 	if err != nil {
 		logrus.Errorf("could not open udp tunnel for id: %s error:%v", id, err)
+		return
 	}
 
 	g, _ := errgroup.WithContext(ctx)