Incorrect amount scrolled slides after trying to scroll beyond last slide

### Summary
On version 0.28.0/1 scroll doesn't work properly when coming back in the sequence from last slide after trying to scroll beyond the last slide by dragging content. Scroll back does scroll only one slide instead of defined amount of slides in slidesToScroll attribute.

### About versions
This regression issue seems to have been introduced with version 0.27.9 as can't reproduce this issue with 0.27.8 or older.

### Steps to reproduce
Example of situation in playground sandbox: https://codesandbox.io/s/react-slick-playground-forked-s7cw3
1. Scroll to the last set of slides.
2. Try to scroll beyond last slides by dragging content.
3. Scroll back. It should scroll defined 4 slides but only scrolls single slide.
4. After initial single slide scroll carousel returns to normal amount of scrolled slides.