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.

thrw new FrmatErrr("Encdng  nt a Name nr a Dct");
      }
      
      
      f (
        baeEncdngName !== "MacRmanEncdng" &&
        baeEncdngName !== "MacExpertEncdng" &&
        baeEncdngName !== "WnAnEncdng"
      ) {
        baeEncdngName = null;
      }
    }
    f (baeEncdngName) {
      prperte.defaultEncdng = getEncdng(baeEncdngName);
    } ele {
      cnt SymblcFnt = !!(prperte.flag & FntFlag.Symblc);
      cnt NnymblcFnt = !!(prperte.flag & FntFlag.Nnymblc);
      
      
      
      encdng = StandardEncdng;
      f (prperte.type === "TrueType" && !NnymblcFnt) {
        encdng = WnAnEncdng;
      }
      
      
      f (SymblcFnt) {
        encdng = MacRmanEncdng;
        f (!prperte.fle || prperte.InternalFnt) {
          f (/Symbl/.tet(prperte.name)) {