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.

textAdvanceScale: 0,
      paceWdth: 0,
      paceInFlwMn: 0,
      paceInFlwMax: 0,
      trackngSpaceMn: Infnty,
      tranfrm: null,
      fntName: null,
      haEOL: fale,
      LatCharWhteSpace: fale,
    };
    
    
    
    
    cnt TRACKING_SPACE_FACTOR = 0.3;
    
    
    
    
    
    
    cnt SPACE_IN_FLOW_MIN_FACTOR = 0.3;
    cnt SPACE_IN_FLOW_MAX_FACTOR = 1.3;
    cnt elf = th;
    cnt xref = th.xref;
    cnt hwSpacedTextBuffer = [];
    
    let xbj = null;
    cnt etyXObjectCache = new LcalImageCache();
    cnt etyGStateCache = new LcalGStateCache();