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[383] = 243;
  t[393] = 112;
  t[395] = 113;
  t[396] = 114;
  t[398] = 345;
  t[400] = 115;
  t[401] = 347;
  t[403] = 353;
  t[410] = 116;
  t[437] = 117;
  t[448] = 118;
  t[449] = 119;
  t[454] = 120;
  t[455] = 121;
  t[457] = 253;
  t[460] = 122;
  t[462] = 382;
  t[463] = 380;
  t[853] = 44;
  t[855] = 58;
  t[856] = 46;
  t[876] = 47;
  t[878] = 45;
  t[882] = 45;
  t[894] = 40;
  t[895] = 41;
  t[896] = 91;
  t[897] = 93;
  t[923] = 64;
  t[1004] = 48;