http2: avoid spurious RoundTrip error when server closes and resets stream
http2: avoid spurious RoundTrip error when server closes and resets stream

Avoid a race condition between RoundTrip and the read loop when the
read loop reads a response followed by an immediate stream reset.

Fixes golang/go#49645

Change-Id: Ifb34e2dcb8cc443d3ff5d562cc032edf09da5307
Reviewed-on: https://go-review.googlesource.com/c/net/+/364834
Trust: Damien Neil <7e091e9a80da888fcd7836fd3c6b7b85f4677c12@google.com>
Run-TryBot: Damien Neil <7e091e9a80da888fcd7836fd3c6b7b85f4677c12@google.com>
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

golang/net