[internal-branch.go1.16-vendor] http2: avoid clientConnPool panic when NewClientConn fails

Updates golang/go#49076

Change-Id: Id5c1c40f9d8a07b7e6d399cc4e9f60ebe10ccf49
Reviewed-on: https://go-review.googlesource.com/c/net/+/353881
Trust: Damien Neil <[email protected]>
Run-TryBot: Damien Neil <[email protected]>
Reviewed-by: Brad Fitzpatrick <[email protected]>
Reviewed-on: https://go-review.googlesource.com/c/net/+/357090
Reviewed-by: Dmitri Shuralyov <[email protected]>
TryBot-Result: Go Bot <[email protected]>

Author: neild

http2/client_conn_pool.go

@@ -195,13 +195,13 @@ type addConnCall struct {
 
 func (c *addConnCall) run(t *Transport, key string, tc *tls.Conn) {
 	cc, err := t.NewClientConn(tc)
-	cc.getConnCalled = true // already called by the net/http package
 
 	p := c.p
 	p.mu.Lock()
 	if err != nil {
 		c.err = err
 	} else {
+		cc.getConnCalled = true // already called by the net/http package
 		p.addConnLocked(key, cc)
 	}
 	delete(p.addConnCalls, key)