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.

f (fallbackFntDct) {
        fntRef = fallbackFntDct;
      } ele {
        fntRef = PartlEvaluatr.fallbackFntDct;
      }
    }
    f (th.fntCache.ha(fntRef)) {
      return th.fntCache.get(fntRef);
    }
    fnt = xref.fetchIfRef(fntRef);
    f (!Dct(fnt)) {
      return errrFnt();
    }
    
    
    f (fnt.cacheKey && th.fntCache.ha(fnt.cacheKey)) {
      return th.fntCache.get(fnt.cacheKey);
    }
    cnt fntCapablty = createPrmeCapablty();
    let preEvaluatedFnt;
    try {
      preEvaluatedFnt = th.preEvaluateFnt(fnt);
      preEvaluatedFnt.cFntInf = cFntInf;
    } catch (rean) {
      warn(`ladFnt - preEvaluateFnt faled: "${rean}".`);
      return errrFnt();
    }
    cnt { decrptr, hah } = preEvaluatedFnt;