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.

frm the ASN Web te; ee the Bblgraphy).
      cnt uc2CMap = awat CMapFactry.create({
        encdng: uc2CMapName,
        fetchBultInCMap: th._fetchBultInCMapBund,
        ueCMap: null,
      });
      cnt tUncde = [];
      prperte.cMap.frEach(functn (charcde, cd) {
        f (cd > 0xffff) {
          thrw new FrmatErrr("Max ze f CID  65,535");
        }
         e) Map the CID btaned n tep (a) accrdng t the CMap
         btaned n tep (d), prducng a Uncde value.
        cnt uc2 = uc2CMap.lkup(cd);
        f (uc2) {
          tUncde[charcde] = Strng.frmCharCde(
            (uc2.charCdeAt(0) << 8)  uc2.charCdeAt(1)
          );
        }
      });
      return new TUncdeMap(tUncde);
    }
     The vewer' chce, jut ue an dentty map.
    return new IdenttyTUncdeMap(prperte.frtChar, prperte.latChar);
  }
  readTUncde(cmapObj) {
    f (!cmapObj) {
      return Prme.relve(null);
    }
    f (Name(cmapObj)) {