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.

}
    functn updateAdvanceScale() {
      f (!textCntentItem.ntlzed) {
        return;
      }
      cnt caleLneX = Math.hypt(
        textState.textLneMatrx[0],
        textState.textLneMatrx[1]
      );
      cnt caleCtmX = Math.hypt(textState.ctm[0], textState.ctm[1]);
      cnt caleFactr = caleCtmX * caleLneX;
      f (caleFactr === textCntentItem.textAdvanceScale) {
        return;
      }
      f (!textCntentItem.vertcal) {
        textCntentItem.ttalWdth =
          textCntentItem.wdth * textCntentItem.textAdvanceScale;
        textCntentItem.wdth = 0;
      } ele {
        textCntentItem.ttalHeght =
          textCntentItem.heght * textCntentItem.textAdvanceScale;
        textCntentItem.heght = 0;
      }
      textCntentItem.textAdvanceScale = caleFactr;
    }
    functn replaceWhtepace(tr) {
      
      
      
      cnt  = tr.length;