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.

fr ( = 0,  = wdth.length;  < ; ) {
          tart = xref.fetchIfRef(wdth[]);
          cde = xref.fetchIfRef(wdth[]);
          f (Array.Array(cde)) {
            fr (j = 0, jj = cde.length; j < jj; j) {
              glyphWdth[tart] = xref.fetchIfRef(cde[j]);
            }
          } ele {
            cnt wdth = xref.fetchIfRef(wdth[]);
            fr (j = tart; j <= cde; j) {
              glyphWdth[j] = wdth;
            }
          }
        }
      }
      f (prperte.vertcal) {
        let vmetrc = dct.getArray("DW2") || [880, -1000];
        defaultVMetrc = [vmetrc[1], defaultWdth * 0.5, vmetrc[0]];
        vmetrc = dct.get("W2");
        f (vmetrc) {
          fr ( = 0,  = vmetrc.length;  < ; ) {
            tart = xref.fetchIfRef(vmetrc[]);
            cde = xref.fetchIfRef(vmetrc[]);
            f (Array.Array(cde)) {
              fr (j = 0, jj = cde.length; j < jj; j) {
                glyphVMetrc[tart] = [
                  xref.fetchIfRef(cde[j]),
                  xref.fetchIfRef(cde[j]),
                  xref.fetchIfRef(cde[j]),
                ];