Attach (recommended) or Link to PDF file here:
[chinese.pdf](https://github.com/mozilla/pdf.js/files/6404389/download.1.pdf)

Configuration:
- Web browser and its version:90.0.4430.93
- Operating system and its version: mac 10.15.5
- PDF.js version: 2.9.146
- Is a browser extension:no

Steps to reproduce the problem:
1. The Chinese in the attachment cannot be rendered

Brower ✅
![image](https://user-images.githubusercontent.com/13477114/116678074-81782a00-a9db-11eb-8719-74f48fcebc2b.png)

PDF.js ❌ [https://mozilla.github.io/pdf.js/web/viewer.html](https://mozilla.github.io/pdf.js/web/viewer.html)
![image](https://user-images.githubusercontent.com/13477114/116678212-a371ac80-a9db-11eb-847f-dd1ad7752c13.png)


What is the expected behavior? (add screenshot)
**The Chinese character can be rendered**
What went wrong? (add screenshot)
**All of the Chinese character cannot be rendered**
Link to a viewer (if hosted on a site other than mozilla.github.io/pdf.js or as Firefox/Chrome extension):

return !missingGlyphs[glyphId];
    }
    if (properties.composite) {
      const cidToGidMap = properties.cidToGidMap || [];
      const isCidToGidMapEmpty = cidToGidMap.length === 0;
      properties.cMap.forEach(function (charCode, cid) {
        if (cid > 0xffff) {
          throw new FormatError("Max size of CID is 65,535");
        }
        let glyphId = -1;
        if (isCidToGidMapEmpty) {
          glyphId = cid;
        } else if (cidToGidMap[cid] !== undefined) {
          glyphId = cidToGidMap[cid];
        }
        if (glyphId >= 0 && glyphId < numGlyphs && hasGlyph(glyphId)) {
          charCodeToGlyphId[charCode] = glyphId;
        }
      });
    } else {
      
      
      const cmapTable = readCmapTable(
        tables.cmap,
        font,
        this.isSymbolicFont,