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.

this.missingFile = true;
    
    
    const name = this.name;
    const type = this.type;
    const subtype = this.subtype;
    let fontName = normalizeFontName(name);
    const stdFontMap = getStdFontMap(),
      nonStdFontMap = getNonStdFontMap();
    const isStandardFont = !!stdFontMap[fontName];
    const isMappedToStandardFont = !!(
      nonStdFontMap[fontName] && stdFontMap[nonStdFontMap[fontName]]
    );
    fontName = stdFontMap[fontName] || nonStdFontMap[fontName] || fontName;
    this.bold = fontName.search(/bold/gi) !== -1;
    this.italic =
      fontName.search(/oblique/gi) !== -1 || fontName.search(/italic/gi) !== -1;
    
    
    this.black = name.search(/Black/g) !== -1;
    
    
    const isNarrow = name.search(/Narrow/g) !== -1;
    
    this.remeasure =
      (!isStandardFont || isNarrow) && Object.keys(this.widths).length > 0;
    if (
      (isStandardFont || isMappedToStandardFont) &&
      type === "CIDFontType2" &&