HS2 HTTP server hangs on large chunked requests

There's a bug in THttpTransport that causes it to hang when sent a large, chunked request.

The issue is that in each call to THttpTransport::read(), it always starts by calling refill() which reads more data off the socket, but for chunked requests each call to read() only processes a single chunk.

So, if more than one chunk is read off the socket at a time, you can end up with more chunks still needing to be processed but no more data to read off the socket, and the next call to THttpTransport::read() will hang when it calls refill().