Monthly and Big Monthly calendars show Blank when reaching the New Year

[rsalsbery]

It was discovered that the Monthly and Big Monthly calendars, currently set to view 6 months in advance are hitting January 1st, 2024. For some reason, this is causing the calendar to load the previous 24 weeks rather than the next 24 weeks causing the calendar to load as empty.

Steps to recreate:

1. Create a Monthly or Big Monthly Calendar
2. Set the Months to Show to reach the New Year (Right now that would be Month to Show set to 6 months)
3. If January 1st is on that month (in the December month block is shows in the last week of that month) the calendar marks it as -24 weeks rather than +24 weeks. This blanks the calendar as it cannot load the previous 24 weeks

Workaround:

Set Months to show to reach only November at the furthest point out.

[Dan-Peck]

Dev Notes:

• The routine that computes the "weeks to show" checks for the "last day of December" to determine its week number in the current year was getting "01" instead of "52"
• This is due to how ISO 8601 handles week determination. Changing "last day of December" to "December 28" will ensure it computes the proper number of weeks in the current year and correct for this anamoly

[Dan-Peck]

Merged in @ aa4c547 and added to the queue for upcoming release to the live site.