Event durationMS is not synced w/ duration value

[arcady-zherdev]

Reported here: https://www.bryntum.com/forum/viewtopic.php?f=44&t=19325

Happens when an event has a non-working period between its start and end dates.

The reason is obvious considering the code:

    get durationMS() {
        const { endDateMS, startDateMS } = this;

        if (endDateMS && startDateMS) {
            return endDateMS - startDateMS;
        }
        else {
            return DH.asMilliseconds(this.duration || 0, this.durationUnit);
        }
    }