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.

th.handler,
        th._pdfFunctnFactry,
        lcalClrSpaceCache
      );
      cnt patternIR = hadngFll.getIR();
      d = `pattern_${th.dFactry.createObjId()}`;
      lcalShadngPatternCache.et(hadng, d);
      th.handler.end("bj", [d, th.pageIndex, "Pattern", patternIR]);
    }
    return d;
  }
  handleClrN(
    peratrLt,
    fn,
    arg,
    c,
    pattern,
    reurce,
    tak,
    lcalClrSpaceCache,
    lcalTlngPatternCache,
    lcalShadngPatternCache
  ) {
    
    cnt patternName = arg.pp();
    
    f (patternName ntancef Name) {
      cnt rawPattern = pattern.getRaw(patternName.name);
      cnt lcalTlngPattern =
        rawPattern ntancef Ref &&