Polyfill: Fix Chinese/Dangi calendar crash when Feb 17 doesn't land in month 1

[jessealama]

Fixes #3158.

When Feb 17 of the ISO year falls in Chinese month 1bis (a leap month after month 1) or month 2, getMonthList() crashes because it assumes Feb 17 is either in month 1 or in the previous year's final month.

The fix checks for 2 first (backing up into month 1 or theoretically 1bis), then for 1bis (backing up to the previous year's last month), letting the existing !== '1' logic advance forward into month 1 as expected.

Known affected years: 7253 (1bis), 7625 (2). Thanks to @fabon-f for digging into this!

[codecov]

Codecov Report

❌ Patch coverage is 17.64706% with 14 lines in your changes missing coverage. Please review.
✅ Project coverage is 97.96%. Comparing base (86a7b46) to head (aa7bb6d).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
polyfill/lib/calendar.mjs	17.64%	13 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3278      +/-   ##
==========================================
- Coverage   98.09%   97.96%   -0.14%     
==========================================
  Files          22       22              
  Lines       10457    10472      +15     
  Branches     1808     1810       +2     
==========================================
+ Hits        10258    10259       +1     
- Misses        182      195      +13     
- Partials       17       18       +1     

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[ptomato]

Great, thanks for digging into this.