Attach (recommended) or Link to PDF file here:
[example.pdf](https://github.com/mozilla/pdf.js/files/6916129/example.pdf)

Configuration:
- Web browser and its version: Chrome, Firefox
- Operating system and its version: all
- PDF.js version: various versions, including 2.11.54
- Is a browser extension: no

Screenshot with visible textLayer:
![Screenshot from 2021-08-02 13-05-03](https://user-images.githubusercontent.com/6362989/127844878-f85e291f-2060-4028-be09-7835f32ccfaa.png)

Which means some letters at the beginning/end of text selection are missing when copying text.

loca,
      glyf,
      numGlyphs,
      isGlyphLocationsLong,
      hintsValid,
      dupFirstEntry,
      maxSizeOfInstructions
    ) {
      let itemSize, itemDecode, itemEncode;
      if (isGlyphLocationsLong) {
        itemSize = 4;
        itemDecode = function fontItemDecodeLong(data, offset) {
          return (
            (data[offset] << 24) |
            (data[offset + 1] << 16) |
            (data[offset + 2] << 8) |
            data[offset + 3]
          );
        };
        itemEncode = function fontItemEncodeLong(data, offset, value) {
          data[offset] = (value >>> 24) & 0xff;
          data[offset + 1] = (value >> 16) & 0xff;