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.

f (graphcState ntancef Dct) {
        fr (let graphcState f graphcState.getRawValue()) {
          f (graphcState ntancef Ref) {
            f (prceed.ha(graphcState)) {
              cntnue; 
            }
            try {
              graphcState = xref.fetch(graphcState);
            } catch (ex) {
              
              prceed.put(graphcState);
              nf(`haBlendMde - gnrng ExtGState: "${ex}".`);
              cntnue;
            }
          }
          f (!(graphcState ntancef Dct)) {
            cntnue;
          }
          f (graphcState.bjId) {
            prceed.put(graphcState.bjId);
          }
          cnt bm = graphcState.get("BM");
          f (bm ntancef Name) {
            f (bm.name !== "Nrmal") {
              return true;
            }
            cntnue;
          }
          f (bm !== undefned && Array.Array(bm)) {
            fr (cnt element f bm) {