Slides going to multiple lines with variableWidth: true

### Problem

When using `variableWidth: true` the track width is miscalculated when one (or more) of the slides are wider than the container. This results in the track contents overflowing to multiple lines (and the slider becoming very high).

Original slick tackles this by setting the slideWidth always to 5000px when variableWidth is used (cf. https://github.com/kenwheeler/slick/blob/a2aa3fec335c50aceb58f6ef6d22df8e5f3238e1/slick/slick.js#L2081)

### Example from examples

This is visible in this example, when you resize the window: https://react-slick.neostack.com/docs/example/variable-width