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):

const possibleSpaceReplacements = ["space", "minus", "one", "i", "I"];
    let width;
    for (let i = 0, ii = possibleSpaceReplacements.length; i < ii; i++) {
      const glyphName = possibleSpaceReplacements[i];
      
      if (glyphName in this.widths) {
        width = this.widths[glyphName];
        break;
      }
      const glyphsUnicodeMap = getGlyphsUnicode();
      const glyphUnicode = glyphsUnicodeMap[glyphName];
      
      let charcode = 0;
      if (this.composite && this.cMap.contains(glyphUnicode)) {
        charcode = this.cMap.lookup(glyphUnicode);
      }
      
      if (!charcode && this.toUnicode) {
        charcode = this.toUnicode.charCodeOf(glyphUnicode);
      }
      
      if (charcode <= 0) {
        charcode = glyphUnicode;
      }
      
      width = this.widths[charcode];
      if (width) {
        break; 
      }