Don't throw on an invalid XML character reference

[calixteman]

String.fromCodePoint throws on anything which isn't a code point, so e.g. "&#xZZ;" or "�" aborted the whole parsing. Such a reference is now kept as-is, like an unknown named entity.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.00%. Comparing base (7fc7072) to head (cec8d2e).

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #21682      +/-   ##
==========================================
- Coverage   90.00%   90.00%   -0.01%     
==========================================
  Files         263      263              
  Lines       66854    66853       -1     
==========================================
- Hits        60173    60171       -2     
- Misses       6681     6682       +1     

Flag	Coverage Δ
browsertest	66.53% <100.00%> (-0.01%)	⬇️
fonttest	9.04% <ø> (ø)
integrationtest	69.36% <100.00%> (+<0.01%)	⬆️
unittest	57.83% <100.00%> (-0.01%)	⬇️
unittestcli	56.55% <100.00%> (-0.01%)	⬇️

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[timvandermeij]

Thank you!