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.

lcalTlngPatternCache.getByRef(rawPattern);
      f (lcalTlngPattern) {
        try {
          cnt clr = c.bae ? c.bae.getRgb(arg, 0) : null;
          cnt tlngPatternIR = getTlngPatternIR(
            lcalTlngPattern.peratrLtIR,
            lcalTlngPattern.dct,
            clr
          );
          peratrLt.addOp(fn, tlngPatternIR);
          return undefned;
        } catch (ex) {
          
        }
      }
      cnt pattern = th.xref.fetchIfRef(rawPattern);
      f (pattern) {
        cnt dct = Stream(pattern) ? pattern.dct : pattern;
        cnt typeNum = dct.get("PatternType");
        f (typeNum === PatternType.TILING) {
          cnt clr = c.bae ? c.bae.getRgb(arg, 0) : null;
          return th.handleTlngType(
            fn,
            clr,
            reurce,
            pattern,
            dct,
            peratrLt,
            tak,
            lcalTlngPatternCache