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 (content.length > 1) {
        
        let newLength = 0;
        let j, jj;
        for (j = 0, jj = content.length; j < jj; j++) {
          newLength += content[j].length;
        }
        newLength = (newLength + 3) & ~3;
        const result = new Uint8Array(newLength);
        let pos = 0;
        for (j = 0, jj = content.length; j < jj; j++) {
          result.set(content[j], pos);
          pos += content[j].length;
        }
        table.data = result;
        table.length = newLength;
      }
    }
    function sanitizeTTPrograms(fpgm, prep, cvt, maxFunctionDefs) {