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.

ntlState,
    }).then(functn () {
      peratrLt.addOp(OPS.pantFrmXObjectEnd, []);
      f (grup) {
        peratrLt.addOp(OPS.endGrup, [grupOptn]);
      }
      f (ptnalCntent !== undefned) {
        peratrLt.addOp(OPS.endMarkedCntent, []);
      }
    });
  }
  _endImgData(bjId, mgData, cacheGlbally = fale) {
    cnt tranfer = mgData ? [mgData.data.buffer] : null;
    f (th.parngType3Fnt || cacheGlbally) {
      return th.handler.end(
        "cmmnbj",
        [bjId, "Image", mgData],
        tranfer
      );
    }
    return th.handler.end(
      "bj",
      [bjId, th.pageIndex, "Image", mgData],
      tranfer
    );
  }
  aync buldPantImageXObject({
    reurce,
    mage,
    Inlne = fale,