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.

if (ttContext.tooComplexToFollowFunctions) {
        return;
      }
      if (ttContext.functionsDefined.length > maxFunctionDefs) {
        warn("TT: more functions defined than expected");
        ttContext.hintsValid = false;
        return;
      }
      for (let j = 0, jj = ttContext.functionsUsed.length; j < jj; j++) {
        if (j > maxFunctionDefs) {
          warn("TT: invalid function id: " + j);
          ttContext.hintsValid = false;
          return;
        }
        if (ttContext.functionsUsed[j] && !ttContext.functionsDefined[j]) {
          warn("TT: undefined function: " + j);
          ttContext.hintsValid = false;
          return;
        }
      }
    }
    function foldTTTable(table, content) {