length is not defined exception when parsing

[Marco Dissel]

I get an error that the length is not defined when parsing this ical
http://www.fcassen.nl/Modules/UitslagenEnStanden/Front/ICal.ashx?id=160

I fixed it by adding the check on the curr.start object:
https://github.com/heskja/MMM-CalendarWeek/blob/master/vendor/ical.js/node-ical.js#L31
if (rule.indexOf('DTSTART') === -1 && curr.start) {