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.

}
    
    const TTOpsStackDeltas = [
      0, 0, 0, 0, 0, 0, 0, 0, -2, -2, -2, -2, 0, 0, -2, -5,
      -1, -1, -1, -1, -1, -1, -1, -1, 0, 0, -1, 0, -1, -1, -1, -1,
      1, -1, -999, 0, 1, 0, -1, -2, 0, -1, -2, -1, -1, 0, -1, -1,
      0, 0, -999, -999, -1, -1, -1, -1, -2, -999, -2, -2, -999, 0, -2, -2,
      0, 0, -2, 0, -2, 0, 0, 0, -2, -1, -1, 1, 1, 0, 0, -1,
      -1, -1, -1, -1, -1, -1, 0, 0, -1, 0, -1, -1, 0, -999, -1, -1,
      -1, -1, -1, -1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
      -2, -999, -999, -999, -999, -999, -1, -1, -2, -2, 0, 0, 0, 0, -1, -1,
      -999, -2, -2, 0, 0, -1, -2, -2, 0, 0, 0, -1, -1, -1, -2];
    
    function sanitizeTTProgram(table, ttContext) {
      let data = table.data;
      let i = 0,
        j,
        n,
        b,
        funcId,
        pc,
        lastEndf = 0,
        lastDeff = 0;
      const stack = [];
      const callstack = [];
      const functionsCalled = [];
      let tooComplexToFollowFunctions = ttContext.tooComplexToFollowFunctions;
      let inFDEF = false,
        ifLevel = 0,
        inELSE = 0;