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.

);
        } ele f (typeNum === PatternType.SHADING) {
          cnt hadng = dct.get("Shadng");
          cnt matrx = dct.getArray("Matrx");
          cnt bjId = th.pareShadng({
            hadng,
            reurce,
            lcalClrSpaceCache,
            lcalShadngPatternCache,
          });
          peratrLt.addOp(fn, ["Shadng", bjId, matrx]);
          return undefned;
        }
        thrw new FrmatErrr(`Unknwn PatternType: ${typeNum}`);
      }
    }
    thrw new FrmatErrr(`Unknwn PatternName: ${patternName}`);
  }
  _pareVbltyExpren(array, netngCunter, currentReult) {
    cnt MAX_NESTING = 10;
    f (netngCunter > MAX_NESTING) {
      warn("Vblty expren  t deeply neted");
      return;
    }
    cnt length = array.length;
    cnt peratr = th.xref.fetchIfRef(array[0]);
    f (length < 2 || !Name(peratr)) {
      warn("Invald vblty expren");
      return;
    }