Motivation:
Because we flow control HEADERS frames, it's possible that an intermediate error can result in a RST_STREAM frame being sent for a frame that the other endpoint is not yet aware of. This is a violation of the spec and will either result in spammy logs at the other endpoint or broken connections.
Modifications:
Modified the HTTP/2 handler so that it only sends RST_STREAM if it has sent at least one HEADERS frame to the remote endpoint for the stream.
Result:
Fixes#4465
8cd259896e