Hi pdfjs team,

Please find attach a really simple pdf file to reproduce the issue.
[Date.pdf](https://github.com/mozilla/pdf.js/files/8242310/Date.pdf)
This pdf contains 4 date fields, One with a default format (dd/mm/yyyy) and the 3 others with custom formats:

    -  dd
    -  mm
    -  yyyy

The expected behavior is that whenever I fill dd field with 16 for instance, then when i focus out that field the value displayed is 16 but I get 01.

This happens for dd field and mm but it's working fine for dd/mm/yyyy and yyyy fields.

The initial values of the pdf are properly displayed, this happens only if I focus one of those fields.

Thank you for your time

Best regards.

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    }
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    const value = this.AFMergeChange(event);
    if (!value) {
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    }
    const checkers = new Map([
      ["9", char => char >= "0" && char <= "9"],
      [
        "A",
        char => ("a" <= char && char <= "z") || ("A" <= char && char <= "Z"),
      ],
      [
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          ("A" <= char && char <= "Z") ||
          ("0" <= char && char <= "9"),
      ],
      ["X", char => true],
    ]);
    function _checkValidity(_value, _cMask) {