fix: Fix panic if initial connection fails

internal/device/watch.go

@@ -211,14 +211,15 @@ func (d *Device) tick() error {
 func (d *Device) connect(opts ...application.ApplicationOption) error {
 	if d.app != nil {
 		_ = d.app.Close(false)
+		d.app = nil
 	}
 	opts = append(
 		opts,
 		application.WithSkipadSleep(config.Default.PlayingInterval),
 		application.WithSkipadRetries(int(time.Minute/config.Default.PlayingInterval)),
 	)
-	d.app = application.NewApplication(opts...)
-	d.app.AddMessageFunc(d.onMessage)
+	app := application.NewApplication(opts...)
+	app.AddMessageFunc(d.onMessage)
 
 	if err := util.Retry(d.ctx, 6, 500*time.Millisecond, func(try uint) error {
 		if err := d.app.Start(d.entry.GetAddr(), d.entry.GetPort()); err != nil {
@@ -239,6 +240,8 @@ func (d *Device) connect(opts ...application.ApplicationOption) error {
 		d.logger.Info("Connected to cast device.")
 	}
 
+	d.app = app
+
 	return nil
 }