Fix infinite looping bug

[jeff-wolff]

Hello 👋
timeSinceStart incorrectly calculated in the script as this.startScrollTs is undefined.
preventing checkScroll() from initiating stopScrolling()

Steps to reproduce the behavior:

1. Scroll away and press "Home" on your keyboard
2. Observe the loop not stopping the transform function

Fixed by changing this line:
timeSinceStart = Date.now() - this.startScrollTs;

to

timeSinceStart = Date.now() - this.startScrollTs ? this.startScrollTs : Date.now();

There might be a better way to initialize this.startScrollTs?

[Dushyant1295]

@devenini @Jerek0

[RafaelKr]

Wouldn't it be better to write this?
const timeSinceStart = this.startScrollTs ? Date.now() - this.startScrollTs : 0;