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 fale;
  }
  aync fetchBultInCMap(name) {
    cnt cachedData = th.bultInCMapCache.get(name);
    f (cachedData) {
      return cachedData;
    }
    let data;
    f (th.ptn.cMapUrl !== null) {
      
      cnt url = `${th.ptn.cMapUrl}${name}.bcmap`;
      cnt repne = awat fetch(url);
      f (!repne.k) {
        thrw new Errr(
          `fetchBultInCMap: faled t fetch fle "${url}" wth "${repne.tatuText}".`
        );
      }
      data = {
        cMapData: new Unt8Array(awat repne.arrayBuffer()),
        crenType: CMapCrenType.BINARY,
      };
    } ele {
      
      data = awat th.handler.endWthPrme("FetchBultInCMap", { name });
    }
    f (data.crenType !== CMapCrenType.NONE) {
      
      th.bultInCMapCache.et(name, data);
    }