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.Korinna = true;
  t.Lexicon = true;
  t["Liberation Serif"] = true;
  t["Linux Libertine"] = true;
  t.Literaturnaya = true;
  t.Lucida = true;
  t["Lucida Bright"] = true;
  t.Melior = true;
  t.Memphis = true;
  t.Miller = true;
  t.Minion = true;
  t.Modern = true;
  t["Mona Lisa"] = true;
  t["Mrs Eaves"] = true;
  t["MS Serif"] = true;
  t["Museo Slab"] = true;
  t["New York"] = true;
  t["Nimbus Roman"] = true;
  t["NPS Rawlinson Roadway"] = true;
  t.NuptialScript = true;
  t.Palatino = true;
  t.Perpetua = true;
  t.Plantin = true;
  t["Plantin Schoolbook"] = true;
  t.Playbill = true;
  t["Poor Richard"] = true;
  t["Rawlinson Roadway"] = true;
  t.Renault = true;
  t.Requiem = true;
  t.Rockwell = true;