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 Object.values(this._glyphCache);
  }
  /**
   * Encode a js string using font encoding.
   * The resulting array contains an encoded string at even positions
   * (can be empty) and a non-encoded one at odd positions.
   * @param {String} a js string.
   * @returns {Array<String>} an array of encoded strings or non-encoded ones.
   */
  encodeString(str) {
    const buffers = [];
    const currentBuf = [];
    
    
    
    
    const hasCurrentBufErrors = () => buffers.length % 2 === 1;
    const getCharCode =
      this.toUnicode instanceof IdentityToUnicodeMap
        ? unicode => this.toUnicode.charCodeOf(unicode)
        : unicode => this.toUnicode.charCodeOf(String.fromCodePoint(unicode));
    for (let i = 0, ii = str.length; i < ii; i++) {
      const unicode = str.codePointAt(i);
      if (unicode > 0xd7ff && (unicode < 0xe000 || unicode > 0xfffd)) {