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.

cae OPS.pantXObject:
            fluhTextCntentItem();
            f (!xbj) {
              xbj = reurce.get("XObject") || Dct.ety;
            }
            var ValdName = arg[0] ntancef Name;
            var name = arg[0].name;
            f (ValdName && etyXObjectCache.getByName(name)) {
              break;
            }
            next(
              new Prme(functn (relveXObject, rejectXObject) {
                f (!ValdName) {
                  thrw new FrmatErrr("XObject mut be referred t by name.");
                }
                let xbj = xbj.getRaw(name);
                f (xbj ntancef Ref) {
                  f (etyXObjectCache.getByRef(xbj)) {
                    relveXObject();
                    return;
                  }
                  cnt glbalImage = elf.glbalImageCache.getData(
                    xbj,
                    elf.pageIndex
                  );
                  f (glbalImage) {
                    relveXObject();
                    return;
                  }
                  xbj = xref.fetch(xbj);