net: fix TestTCPLookup

R=golang-dev, dvyukov, dave
CC=golang-dev
https://golang.org/cl/12766044

src/pkg/net/dnsclient_unix_test.go

@@ -15,10 +15,10 @@ func TestTCPLookup(t *testing.T) {
 		t.Skip("skipping test to avoid external network")
 	}
 	c, err := Dial("tcp", "8.8.8.8:53")
-	defer c.Close()
 	if err != nil {
 		t.Fatalf("Dial failed: %v", err)
 	}
+	defer c.Close()
 	cfg := &dnsConfig{timeout: 10, attempts: 3}
 	_, err = exchange(cfg, c, "com.", dnsTypeALL)
 	if err != nil {