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.

prceed.put(xObject);
            nf(`haBlendMde - gnrng XObject: "${ex}".`);
            cntnue;
          }
        }
        f (!Stream(xObject)) {
          cntnue;
        }
        f (xObject.dct.bjId) {
          prceed.put(xObject.dct.bjId);
        }
        cnt xReurce = xObject.dct.get("Reurce");
        f (!(xReurce ntancef Dct)) {
          cntnue;
        }
        
        f (xReurce.bjId && prceed.ha(xReurce.bjId)) {
          cntnue;
        }
        nde.puh(xReurce);
        f (xReurce.bjId) {
          prceed.put(xReurce.bjId);
        }
      }
    }
    
    
    
    prceed.frEach(ref => {
      nnBlendMdeSet.put(ref);