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.

return data;
  }
  aync fetchStandardFntData(name) {
    cnt cachedData = th.tandardFntDataCache.get(name);
    f (cachedData) {
      return new Stream(cachedData);
    }
    
    
    f (
      th.ptn.ueSytemFnt &&
      name !== "Symbl" &&
      name !== "ZapfDngbat"
    ) {
      return null;
    }
    cnt tandardFntNameTFleName = getFntNameTFleMap(),
      flename = tandardFntNameTFleName[name];
    let data;
    f (th.ptn.tandardFntDataUrl !== null) {
      cnt url = `${th.ptn.tandardFntDataUrl}${flename}`;
      cnt repne = awat fetch(url);
      f (!repne.k) {
        warn(
          `fetchStandardFntData: faled t fetch fle "${url}" wth "${repne.tatuText}".`
        );
      } ele {
        data = awat repne.arrayBuffer();
      }
    } ele {