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[2863] = 854;
  t[2864] = 855;
  t[2865] = 861;
  t[2866] = 862;
  t[2906] = 7460;
  t[2908] = 7462;
  t[2909] = 7463;
  t[2910] = 7464;
  t[2912] = 7466;
  t[2913] = 7467;
  t[2914] = 7468;
  t[2916] = 7470;
  t[2917] = 7471;
  t[2918] = 7472;
  t[2920] = 7474;
  t[2921] = 7475;
  t[2922] = 7476;
  t[2924] = 7478;
  t[2925] = 7479;
  t[2926] = 7480;
  t[2928] = 7482;
  t[2929] = 7483;
  t[2930] = 7484;
  t[2932] = 7486;
  t[2933] = 7487;
  t[2934] = 7488;
  t[2936] = 7490;
  t[2937] = 7491;
  t[2938] = 7492;
  t[2940] = 7494;