HTTP2: fix crash from assertion

In general the protocolHandler isn't deleted unless
the channel is being destructed. So instead of reset()ing
the pointer we keep it around.

Also update the http2protocolhandler to mimic the http1
handler a little closer: shutting down the channel in
receiveReply if there's no reply/activeStreams, and not
calling receiveReply at all if there's no activeStreams.

Pick-to: 5.15
Change-Id: I702547f594deb6b0c1384068f7e93e560527e8e2
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@qt.io>

src/network/access/qhttp2protocolhandler.cpp

@@ -264,7 +264,8 @@ void QHttp2ProtocolHandler::_q_uploadDataDestroyed(QObject *uploadData)
 
 void QHttp2ProtocolHandler::_q_readyRead()
 {
-    _q_receiveReply();
+    if (!goingAway || activeStreams.size())
+        _q_receiveReply();
 }
 
 void QHttp2ProtocolHandler::_q_receiveReply()
@@ -272,6 +273,11 @@ void QHttp2ProtocolHandler::_q_receiveReply()
     Q_ASSERT(m_socket);
     Q_ASSERT(m_channel);
 
+    if (goingAway && activeStreams.isEmpty()) {
+        m_channel->close();
+        return;
+    }
+
     while (!goingAway || activeStreams.size()) {
         const auto result = frameReader.read(*m_socket);
         switch (result) {

src/network/access/qhttpnetworkconnectionchannel.cpp

@@ -995,7 +995,6 @@ void QHttpNetworkConnectionChannel::_q_error(QAbstractSocket::SocketError socket
                         && switchedToHttp2)) {
                     auto h2Handler = static_cast<QHttp2ProtocolHandler *>(protocolHandler.data());
                     h2Handler->handleConnectionClosure();
-                    protocolHandler.reset();
                 }
             }
             return;