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.

const ttcTag = ttc.getString(4);
      assert(ttcTag === "ttcf", "Must be a TrueType Collection font.");
      const majorVersion = ttc.getUint16();
      const minorVersion = ttc.getUint16();
      const numFonts = ttc.getInt32() >>> 0;
      const offsetTable = [];
      for (let i = 0; i < numFonts; i++) {
        offsetTable.push(ttc.getInt32() >>> 0);
      }
      const header = {
        ttcTag,
        majorVersion,
        minorVersion,
        numFonts,
        offsetTable,
      };
      switch (majorVersion) {
        case 1:
          return header;
        case 2:
          header.dsigTag = ttc.getInt32() >>> 0;
          header.dsigLength = ttc.getInt32() >>> 0;
          header.dsigOffset = ttc.getInt32() >>> 0;
          return header;
      }
      throw new FormatError(
        `Invalid TrueType Collection majorVersion: ${majorVersion}.`
      );
    }
    function readTrueTypeCollectionData(ttc, fontName) {