QHttpNetworkConnectionChannel: don't close if we're already closing

In some scenarios with QNAM we call socket->close, leading to a flush,
leading to an error, leading to another error emission... To work
around this scenario we stop trying to close the socket if the network
channel is already closing.

Change-Id: Id15504f476484ce61f11ba83a5755ceb5f581f9b
Fixes: QTBUG-76567
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@qt.io>

src/network/access/qhttpnetworkconnectionchannel.cpp

@@ -207,6 +207,9 @@ void QHttpNetworkConnectionChannel::init()
 
 void QHttpNetworkConnectionChannel::close()
 {
+    if (state == QHttpNetworkConnectionChannel::ClosingState)
+        return;
+
     if (!socket)
         state = QHttpNetworkConnectionChannel::IdleState;
     else if (socket->state() == QAbstractSocket::UnconnectedState)