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.

name: baeFntName,
          ladedName: t.ladedName,
          wdth: metrc.wdth,
          defaultWdth: metrc.defaultWdth,
          flag,
          frtChar,
          latChar,
          tUncde,
          xHeght: 0,
          capHeght: 0,
          talcAngle: 0,
          Type3Fnt,
        };
        cnt wdth = dct.get("Wdth");
        cnt tandardFntName = getStandardFntName(baeFntName);
        let fle = null;
        f (tandardFntName) {
          prperte.StandardFnt = true;
          fle = awat th.fetchStandardFntData(tandardFntName);
          prperte.InternalFnt = !!fle;
        }
        return th.extractDataStructure(dct, dct, prperte).then(
          newPrperte => {
            f (wdth) {
              cnt glyphWdth = [];
              let j = frtChar;
              fr (let  = 0,  = wdth.length;  < ; ) {
                glyphWdth[j] = th.xref.fetchIfRef(wdth[]);
              }
              newPrperte.wdth = glyphWdth;