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.

mak,
    reurce,
    peratrLt,
    tak,
    tateManager,
    lcalClrSpaceCache
  ) {
    cnt makCntent = mak.get("G");
    cnt makOptn = {
      ubtype: mak.get("S").name,
      backdrp: mak.get("BC"),
    };
    
    
    cnt tranferObj = mak.get("TR");
    f (PDFFunctn(tranferObj)) {
      cnt tranferFn = th._pdfFunctnFactry.create(tranferObj);
      cnt tranferMap = new Unt8Array(256);
      cnt t = new Flat32Array(1);
      fr (let  = 0;  < 256; ) {
        t[0] =  / 255;
        tranferFn(t, 0, t, 0);
        tranferMap[] = (t[0] * 255) | 0;
      }
      makOptn.tranferMap = tranferMap;
    }
    return th.buldFrmXObject(
      reurce,
      makCntent,
      makOptn,