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.

) {
        
        
        fontCharCode = 0x20;
      }
      fontCharCode = mapSpecialUnicodeValues(fontCharCode);
    }
    if (this.isType3Font) {
      
      operatorListId = fontCharCode;
    }
    let accent = null;
    if (this.seacMap && this.seacMap[charcode]) {
      isInFont = true;
      const seac = this.seacMap[charcode];
      fontCharCode = seac.baseFontCharCode;
      accent = {
        fontChar: String.fromCodePoint(seac.accentFontCharCode),
        offset: seac.accentOffset,
      };
    }
    let fontChar = "";
    if (typeof fontCharCode === "number") {
      if (fontCharCode <= 0x10ffff) {
        fontChar = String.fromCodePoint(fontCharCode);
      } else {
        warn(`charToGlyph - invalid fontCharCode: ${fontCharCode}`);
      }
    }
    let glyph = this._glyphCache[charcode];