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.

return;
                }
                f (elf.ptn.gnreErrr) {
                  
                  
                  elf.handler.end("UnupprtedFeature", {
                    featureId: UNSUPPORTED_FEATURES.errrXObject,
                  });
                  warn(`getOperatrLt - gnrng XObject: "${rean}".`);
                  return;
                }
                thrw rean;
              })
            );
            return;