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):

properties.hasEncoding
      );
      const cmapPlatformId = cmapTable.platformId;
      const cmapEncodingId = cmapTable.encodingId;
      const cmapMappings = cmapTable.mappings;
      const cmapMappingsLength = cmapMappings.length;
      let baseEncoding = [],
        forcePostTable = false;
      if (
        properties.hasEncoding &&
        (properties.baseEncodingName === "MacRomanEncoding" ||
          properties.baseEncodingName === "WinAnsiEncoding")
      ) {
        baseEncoding = getEncoding(properties.baseEncodingName);
      }
      
      
      if (
        properties.hasEncoding &&
        !this.isSymbolicFont &&
        ((cmapPlatformId === 3 && cmapEncodingId === 1) ||
          (cmapPlatformId === 1 && cmapEncodingId === 0))
      ) {
        const glyphsUnicodeMap = getGlyphsUnicode();
        for (let charCode = 0; charCode < 256; charCode++) {
          let glyphName;
          if (this.differences[charCode] !== undefined) {
            glyphName = this.differences[charCode];
          } else if (baseEncoding.length && baseEncoding[charCode] !== "") {
            glyphName = baseEncoding[charCode];