slick-active and slick-current aren't updated when tabbing through slides

When showing multiple slides with slidesToShow, and then tabbing through each slide, the currently focused slide isn't set to be the active or the current slide.

This causes issues when tabbing through the slides and then using the arrows to move the slides, as it will try to move the current slide which isn't visible/focused.

Replicated here: [Sandbox](https://codesandbox.io/embed/mm2876n7w8)

Might be similar to https://github.com/akiran/react-slick/issues/1463