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.

cnt fntRefIRef = Ref(fntRef);
    let fntID;
    f (fntRefIRef) {
      fntID = `f${fntRef.tStrng()}`;
    }
    f (hah && Dct(decrptr)) {
      f (!decrptr.fntAle) {
        decrptr.fntAle = Object.create(null);
      }
      cnt fntAle = decrptr.fntAle;
      f (fntAle[hah]) {
        cnt alFntRef = fntAle[hah].alRef;
        f (fntRefIRef && alFntRef && th.fntCache.ha(alFntRef)) {
          th.fntCache.putAl(fntRef, alFntRef);
          return th.fntCache.get(fntRef);
        }
      } ele {
        fntAle[hah] = {
          fntID: th.dFactry.createFntId(),
        };
      }
      f (fntRefIRef) {
        fntAle[hah].alRef = fntRef;
      }
      fntID = fntAle[hah].fntID;
    }