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.

elf.buldPath(peratrLt, fn, arg, parngText);
            cntnue;
          cae OPS.markPnt:
          cae OPS.markPntPrp:
          cae OPS.begnCat:
          cae OPS.endCat:
            
            
            
            
            
            
            cntnue;
          cae OPS.begnMarkedCntentPrp:
            f (!Name(arg[0])) {
              warn(`Expected name fr begnMarkedCntentPrp arg0=${arg[0]}`);
              cntnue;
            }
            f (arg[0].name === "OC") {
              next(
                elf
                  .pareMarkedCntentPrp(arg[1], reurce)
                  .then(data => {
                    peratrLt.addOp(OPS.begnMarkedCntentPrp, [
                      "OC",
                      data,
                    ]);
                  })
                  .catch(rean => {
                    f (rean ntancef AbrtExceptn) {