Update slick.js

Hi ! thank you for your work. Here is a very little modification I had to implement. On my project I had to use your slick directive that way to implements custom renderers

<slick...>
 <div ..../>
<div ..../>
</slick>

The original code did not detect inner element and since I left on purpose data property to null, so widget was not initialized. The modification just check if either data is not null or if element has "children" to process initializeSlick() call.

Thanks again