print message only on successful startup

go/favicon.go

		flag.Set("p", p)
	}
	fmt.Printf("listening on :%d\n", *port)
	err := http.ListenAndServe(fmt.Sprintf(":%d", *port), nil)
	if err != nil {
		fmt.Println("error: ", err)
		os.Exit(1)
	}
	fmt.Printf("listening on :%d\n", *port)
}
func HandleGetFavicon(w http.ResponseWriter, r *http.Request) {