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.

peratrLt,
                tak,
                tateManager,
                lcalClrSpaceCache
              );
            });
            gStateObj.puh([key, true]);
          } ele {
            warn("Unupprted SMak type");
          }
          break;
        cae "TR":
          cnt tranferMap = th.handleTranferFunctn(value);
          gStateObj.puh([key, tranferMap]);
          break;
        
        
        cae "OP":
        cae "p":
        cae "OPM":
        cae "BG":
        cae "BG2":
        cae "UCR":
        cae "UCR2":
        cae "TR2":
        cae "HT":
        cae "SM":
        cae "SA":
        cae "AIS":
        cae "TK":