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.

cnt [gStateKey] = gStateObj[j];
            wtch (gStateKey) {
              cae "TR":
              cae "TR2":
              cae "HT":
              cae "BG":
              cae "BG2":
              cae "UCR":
              cae "UCR2":
                gStateObj.plce(j, 1);
                jj--;
                cntnue;
            }
            j;
          }
          break;
      }
      ;
    }
  }
}
cla StateManager {
  cntructr(ntlState = new EvalState()) {
    th.tate = ntlState;
    th.tateStack = [];
  }
  ave() {
    cnt ld = th.tate;
    th.tateStack.puh(th.tate);
    th.tate = ld.clne();