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):

}
      }
      
      
      if (cidToGidMap) {
        for (const charCode in map) {
          const cid = map[charCode];
          if (cidToGidMap[cid] !== undefined) {
            map[+charCode] = cidToGidMap[cid];
          }
        }
      }
      const isIdentityUnicode = this.toUnicode instanceof IdentityToUnicodeMap;
      if (!isIdentityUnicode) {
        this.toUnicode.forEach(function (charCode, unicodeCharCode) {
          map[+charCode] = unicodeCharCode;
        });
      }
      this.toFontChar = map;
      this.toUnicode = new ToUnicodeMap(map);
    } else if (/Symbol/i.test(fontName)) {
      this.toFontChar = buildToFontChar(
        SymbolSetEncoding,
        getGlyphsUnicode(),
        this.differences
      );
    } else if (/Dingbats/i.test(fontName)) {
      if (/Wingdings/i.test(name)) {
        warn("Non-embedded Wingdings font, falling back to ZapfDingbats.");
      }