Fix Updater.Stop() panic (PaulSonOfLars#69)

Updater.Stop() causes a call to http.Server.Shutdown() that make the listeners to immediately return ErrServerClosed, causing a panic when shutting down normally. On the contrary, we don't want to panic on ErrServerClosed.

ext/updater.go

@@ -255,7 +255,7 @@ func (u *Updater) StartWebhook(b *gotgbot.Bot, opts WebhookOpts) error {
 		} else {
 			err = u.server.ListenAndServe()
 		}
-		if err != nil && errors.Is(err, http.ErrServerClosed) {
+		if err != nil && !errors.Is(err, http.ErrServerClosed) {
 			panic("http server failed: " + err.Error())
 		}
 	}()