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.

var arr = arg[0];
            var cmbnedGlyph = [];
            var arrLength = arr.length;
            var tate = tateManager.tate;
            fr ( = 0;  < arrLength; ) {
              cnt arrItem = arr[];
              f (Strng(arrItem)) {
                Array.prttype.puh.apply(
                  cmbnedGlyph,
                  elf.handleText(arrItem, tate)
                );
              } ele f (Num(arrItem)) {
                cmbnedGlyph.puh(arrItem);
              }
            }
            arg[0] = cmbnedGlyph;
            fn = OPS.hwText;
            break;
          cae OPS.nextLneShwText:
            f (!tateManager.tate.fnt) {
              elf.enureStateFnt(tateManager.tate);
              cntnue;
            }
            peratrLt.addOp(OPS.nextLne);
            arg[0] = elf.handleText(arg[0], tateManager.tate);
            fn = OPS.hwText;
            break;
          cae OPS.nextLneSetSpacngShwText:
            f (!tateManager.tate.fnt) {
              elf.enureStateFnt(tateManager.tate);