When a client receives a HEADER frame with a END_STREAM flag,
clientConn.streamByID closes the stream before processing the headers
which may contain a full non-error response. This causes the request's
bodyWriter cancelation to race with the response.

Closing the stream after processing headers allows the response to be
available before the bodyWriter is canceled.

Updates golang/go#20521

Change-Id: I70740e88f75240836e922163a54a6cd89535f7b3
Reviewed-on: https://go-review.googlesource.com/70510
Run-TryBot: Emmanuel Odeke <emm.odeke@gmail.com>
Reviewed-by: Tom Bergan <tombergan@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>