Avoid infinite loop in getNextFromDate

Reproduce issue with this:

var CronTime = require('cron').CronTime;
var validSource = '0 * * * * *';
var validTimezone = 'UTC';
var invalidFromDate = new Date('2014-12-01-bogus');
var date = new CronTime(validSource, validTimezone)._getNextDateFrom(invalidFromDate);
console.log(date.getTime());