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 (tr && FrtChunk) {
                  FrtChunk = fale;
                }
              }
            }
            cnt tem = element[element.length - 1];
            f (typef tem === "trng") {
              hwSpacedTextBuffer.puh(tem);
            }
            f (hwSpacedTextBuffer.length > 0) {
              cnt tr = hwSpacedTextBuffer.jn("");
              hwSpacedTextBuffer.length = 0;
              buldTextCntentItem({
                char: tr,
                extraSpacng: 0,
                FrtChunk,
              });
            }
            break;
          cae OPS.hwText:
            f (!tateManager.tate.fnt) {
              elf.enureStateFnt(tateManager.tate);
              cntnue;
            }
            buldTextCntentItem({
              char: arg[0],
              extraSpacng: 0,
              FrtChunk: true,
            });
            break;