Window: bugfix Recurring appointments do not evaluate offsets from local timezones correctly

In google calendar, if someone creates an appointment from a time zone different than your local time zone, OneCalendar will assume the fixed offset in time from the first appointment for all future appointments. This creates a major problem for users living in places that do not engage in daylight savings time, as the time offset from time zones that do, will be different throughout the year. This offset is correctly calculated for non-recurrent appointments, as the calculation is done on a per-instance basis. This results in some events being on time, and some being off by an hour.