Handle event undefined in initMoveObserver

[yakkomajuri]

A quick suggestion for handling a case where this expression:

isTouchEvent(event)
        ? event.changedTouches[0]
        : event;

returns undefined, causing an error when trying to access clientX here:

const { clientX, clientY } = isTouchEvent(event)
    ? event.changedTouches[0]
    : event;

Appears to be the cause of this error: https://sentry.io/share/issue/f01259a2c753426cbfccad01c30a102b/

Happy to look into it more deeply if the approach is off - my objective here is to open a discussion via a PR rather than an issue.

[Yuyz0112]

Thanks! @yakkomajuri

I think safely access the index from an array is always reasonable. And of course, it will be cool if we can find what actually happened to let the event be nullable.