fix(menu): proper setting of leftShowing flag
fix(menu): proper setting of leftShowing flag

* fix(menu): proper setting of leftShowing flag

* fix(menu): optimized setting of leftShowing and rightShowing flag

yanzhihong23/ionic-nono,yanzhihong23/ionic-nono,VinceOPS/ionic,yanzhihong23/ionic-nono,yanzhihong23/ionic-nono,VinceOPS/ionic,VinceOPS/ionic,VinceOPS/ionic