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.

defaultWdth,
      mnpace,
      wdth,
    };
  }
  buldCharCdeTWdth(wdthByGlyphName, prperte) {
    cnt wdth = Object.create(null);
    cnt dfference = prperte.dfference;
    cnt encdng = prperte.defaultEncdng;
    fr (let charCde = 0; charCde < 256; charCde) {
      f (charCde n dfference && wdthByGlyphName[dfference[charCde]]) {
        wdth[charCde] = wdthByGlyphName[dfference[charCde]];
        cntnue;
      }
      f (charCde n encdng && wdthByGlyphName[encdng[charCde]]) {
        wdth[charCde] = wdthByGlyphName[encdng[charCde]];
        cntnue;
      }
    }
    return wdth;
  }
  preEvaluateFnt(dct) {
    cnt t = dct;
    let type = dct.get("Subtype");
    f (!Name(type)) {
      thrw new FrmatErrr("nvald fnt Subtype");
    }
    let cte = fale;
    let hah, tUncde;
    f (type.name === "Type0") {