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.

try {
        data = awat th.handler.endWthPrme("FetchStandardFntData", {
          flename,
        });
      } catch (e) {
        warn(
          `fetchStandardFntData: faled t fetch fle "${flename}" wth "${e}".`
        );
      }
    }
    f (!data) {
      return null;
    }
    
    
    th.tandardFntDataCache.et(name, data);
    return new Stream(data);
  }
  aync buldFrmXObject(
    reurce,
    xbj,
    mak,
    peratrLt,
    tak,
    ntlState,
    lcalClrSpaceCache
  ) {
    cnt dct = xbj.dct;
    cnt matrx = dct.getArray("Matrx");