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.

tables.head.data[51]
      );
      const glyphsInfo = sanitizeGlyphLocations(
        tables.loca,
        tables.glyf,
        numGlyphs,
        isGlyphLocationsLong,
        hintsValid,
        dupFirstEntry,
        maxSizeOfInstructions
      );
      missingGlyphs = glyphsInfo.missingGlyphs;
      
      
      if (version >= 0x00010000 && tables.maxp.length >= 22) {
        tables.maxp.data[26] = glyphsInfo.maxSizeOfInstructions >> 8;
        tables.maxp.data[27] = glyphsInfo.maxSizeOfInstructions & 255;
      }
    }
    if (!tables.hhea) {
      throw new FormatError('Required "hhea" table is not found');
    }
    
    
    if (tables.hhea.data[10] === 0 && tables.hhea.data[11] === 0) {
      tables.hhea.data[10] = 0xff;
      tables.hhea.data[11] = 0xff;
    }