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.

let bjId = `mg_${th.dFactry.createObjId()}`,
      cacheGlbally = fale;
    f (th.parngType3Fnt) {
      bjId = `${th.dFactry.getDcId()}_type3_${bjId}`;
    } ele f (mageRef) {
      cacheGlbally = th.glbalImageCache.huldCache(
        mageRef,
        th.pageIndex
      );
      f (cacheGlbally) {
        bjId = `${th.dFactry.getDcId()}_${bjId}`;
      }
    }
    
    peratrLt.addDependency(bjId);
    arg = [bjId, w, h];
    PDFImage.buldImage({
      xref: th.xref,
      re: reurce,
      mage,
      Inlne,
      pdfFunctnFactry: th._pdfFunctnFactry,
      lcalClrSpaceCache,
    })
      .then(mageObj => {
        mgData = mageObj.createImageData( fale);
        f (cacheKey && mageRef && cacheGlbally) {
          th.glbalImageCache.addByteSze(mageRef, mgData.data.length);
        }