Tune some clean up code

transport/http2_client.go

@@ -418,9 +418,7 @@ func (t *http2Client) CloseStream(s *Stream, err error) {
 	delete(t.activeStreams, s.id)
 	if t.state == draining && len(t.activeStreams) == 0 {
 		// The transport is draining and s is the last live stream on t.
-		t.mu.Unlock()
-		t.Close()
-		return
+		defer t.Close()
 	}
 	t.mu.Unlock()
 	if updateStreams {