QNetworkAccessManager: Stack overflow crash when proxy server closes connection shortly after connecting using spdy/http2

(presumably affects all platforms, but not tested)

Tail of the stack trace is attached.

The steps needed:

1. Use QNAM with a proxy which will reject you quickly (I use CCproxy with my IP not in the allowed list)
2. Needs to have the SPDY or H2 attribute enabled on the QNetworkRequest
3. Start connecting to any address (possibly needs to be an endpoint with TLS)
4. Get rejected by the proxy / have the proxy close the connection
5. Crash due to stack overflow

The problem is that it will then recursively emit errors until it crashes (the recursion being due to QHttpNetworkConnectionChannel::close trying to close the socket, which triggers a flush, which triggers an error emission which loops back to the aforementioned close() method).