slick-cloned slides visible if slidesToDisplay > slide count

In recent versions, if slidesToShow is set to a value greater than the number of slides, all of the slick-cloned slides will be visible.

To replicate:
in the PlayGround (https://codesandbox.io/s/ppwkk5l6xx) update the settings:
```
var settings = {
dots: true,
slidesToShow: 5
};
```

Version 0.21.0 does not behave this way. With version 0.21.0 if the slidesToShow is greater than the number of slides, it does not create the slick-cloned slides.