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[307] = 966;
  t[308] = 8215;
  t[309] = 8252;
  t[310] = 8319;
  t[311] = 8359;
  t[312] = 8592;
  t[313] = 8593;
  t[337] = 9552;
  t[493] = 1039;
  t[494] = 1040;
  t[705] = 1524;
  t[706] = 8362;
  t[710] = 64288;
  t[711] = 64298;
  t[759] = 1617;
  t[761] = 1776;
  t[763] = 1778;
  t[775] = 1652;
  t[777] = 1764;
  t[778] = 1780;
  t[779] = 1781;
  t[780] = 1782;
  t[782] = 771;
  t[783] = 64726;
  t[786] = 8363;
  t[788] = 8532;
  t[790] = 768;
  t[791] = 769;
  t[792] = 768;
  t[795] = 803;