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.

cnt glbalImage = elf.glbalImageCache.getData(
                    xbj,
                    elf.pageIndex
                  );
                  f (glbalImage) {
                    peratrLt.addDependency(glbalImage.bjId);
                    peratrLt.addOp(glbalImage.fn, glbalImage.arg);
                    relveXObject();
                    return;
                  }
                  xbj = xref.fetch(xbj);
                }
                f (!Stream(xbj)) {
                  thrw new FrmatErrr("XObject huld be a tream");
                }
                cnt type = xbj.dct.get("Subtype");
                f (!Name(type)) {
                  thrw new FrmatErrr("XObject huld have a Name ubtype");
                }
                f (type.name === "Frm") {
                  tateManager.ave();
                  elf
                    .buldFrmXObject(
                      reurce,
                      xbj,
                      null,
                      peratrLt,
                      tak,
                      tateManager.tate.clne(),
                      lcalClrSpaceCache