Attach (recommended) or Link to PDF file here:
[test.pdf](https://github.com/mozilla/pdf.js/files/6270827/test.pdf)
Configuration:
- Web browser and its version:chrome 89
- Operating system and its version:win10
- PDF.js version: 2.4/2.7/2.8 no working
- Is a browser extension: no 

What is the expected behavior? (add screenshot)
![image](https://user-images.githubusercontent.com/18545199/113852392-1ae26080-97cf-11eb-9dc9-0cecf52d267b.png)

What went wrong? (add screenshot)
![1617791294(1)](https://user-images.githubusercontent.com/18545199/113852355-10c06200-97cf-11eb-8672-598750f1093a.jpg)


console this log : **FormatError: TrueType Collection does not contain "DCWGQU+CambriaMath" font** 

any solution?thanks
}
      }
      
      if (!charsCache) {
        charsCache = this.charsCache = Object.create(null);
      }
      glyphs = [];
      var charsCacheKey = chars;
      var i = 0,
        ii;
      if (this.cMap) {
        
        
        var c = Object.create(null);
        while (i < chars.length) {
          this.cMap.readCharCode(chars, i, c);
          charcode = c.charcode;
          var length = c.length;
          i += length;
          
          var isSpace = length === 1 && chars.charCodeAt(i - 1) === 0x20;
          glyph = this._charToGlyph(charcode, isSpace);
          glyphs.push(glyph);
        }
      } else {
        for (i = 0, ii = chars.length; i < ii; ++i) {
          charcode = chars.charCodeAt(i);
          glyph = this._charToGlyph(charcode, charcode === 0x20);
          glyphs.push(glyph);
        }