HTTP2 channel reconnects silently without "user space" notification

Hi,

I faced issue with Qt HTTP2 implementation. If channel is disconnected while communication from server, in HTTP2 handler there is automatical channel recovery mechanism. This idea pretty solid, but the problem is that userspace doesn't see this and cannot re-send data to server, for example. As simple solution I suggest to trigger QNetworkReply::error once with QNetworkReply::TemporaryNetworkFailureError, when connection is broken. It will give possibility for library users to re-send required data to server.

Steps:

1. Start server from attached tarball
2. Start client
3. Observe messages conversation
4. Stop server
5. Start server

Oserved behaivor:

4. Client silently reconnect to server but doesn't send any request

Expected behaivor:

4. Error occured on client side