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):

) {
        
        
        fontCharCode = 0x20;
      }
      fontCharCode = mapSpecialUnicodeValues(fontCharCode);
    }
    if (this.isType3Font) {
      
      operatorListId = fontCharCode;
    }
    let accent = null;
    if (this.seacMap && this.seacMap[charcode]) {
      isInFont = true;
      const seac = this.seacMap[charcode];
      fontCharCode = seac.baseFontCharCode;
      accent = {
        fontChar: String.fromCodePoint(seac.accentFontCharCode),
        offset: seac.accentOffset,
      };
    }
    let fontChar = "";
    if (typeof fontCharCode === "number") {
      if (fontCharCode <= 0x10ffff) {
        fontChar = String.fromCodePoint(fontCharCode);
      } else {
        warn(`charToGlyph - invalid fontCharCode: ${fontCharCode}`);
      }
    }
    let glyph = this._glyphCache[charcode];