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.

t.Corona = true;
  t.Ecotype = true;
  t.Egyptienne = true;
  t.Elephant = true;
  t.Excelsior = true;
  t.Fairfield = true;
  t["FF Scala"] = true;
  t.Folkard = true;
  t.Footlight = true;
  t.FreeSerif = true;
  t["Friz Quadrata"] = true;
  t.Garamond = true;
  t.Gentium = true;
  t.Georgia = true;
  t.Gloucester = true;
  t["Goudy Old Style"] = true;
  t["Goudy Schoolbook"] = true;
  t["Goudy Pro Font"] = true;
  t.Granjon = true;
  t["Guardian Egyptian"] = true;
  t.Heather = true;
  t.Hercules = true;
  t["High Tower Text"] = true;
  t.Hiroshige = true;
  t["Hoefler Text"] = true;
  t["Humana Serif"] = true;
  t.Imprint = true;
  t["Ionic No. 5"] = true;
  t.Janson = true;
  t.Joanna = true;