afterSlideLoad code is not executing on first slide

Hi and thank you for creating fullpage. I've created a [CodePen](https://codepen.io/Carrly/pen/LQPLez) with my issue.

I'm using fullpage with the horizontal slides. I have some animations happening on each slide load. I'm triggering those animations using `afterSlideLoad`.

The first slide doesn't load my animations and `console.log(slideIndex)` doesn't return anything for that first slide. This just happens when you initially load or reload the page.

It's happening in all browsers so it's not a browser issue. I hope you can help me, thanks!