`infinite` doesn't play nicely with `variableWidth` and `focusOnSelect`

### Intention
I am trying to create an **infinite** slider that will display a set of items, where the items have **variable width** and a click item gets **focus on select** (moves to left edge of slider component) when clicked.

### Problem
In many (but not all cases), Slick React scrolls to cloned version of the clicked item, instead of the item itself.
[See example](https://codesandbox.io/s/react-slick-playground-forked-0t02t).

What's working:
* From index 0 (start), click on item -1 (left of item 0, visible because `overflow: visible`)
* From item -1, click on item 0
* From item -1, click on item 1
* From item -1, click on item 2

What's not working:
* From item 0, click on item 1 => scrolls to wrong item
* From item 1, click on item 2 => scrolls to wrong item
* From item -1, click on item -2 => scrolls to wrong item

(these lists are not exhaustive, obviously, just as an example)