Attach (recommended) or Link to PDF file here:
[test.pdf](https://github.com/mozilla/pdf.js/files/6715502/test.pdf)

Configuration:
- Web browser and its version: Google Chrome Version 91.0.4472.114 
- Operating system and its version: Windows 10 Enterprise
- PDF.js version: 
- Is a browser extension: yes

Steps to reproduce the problem:
1. download file
2. open file



What is the expected behavior? (add screenshot)
show symbol
![image](https://user-images.githubusercontent.com/50500976/123409847-55ca8800-d5b7-11eb-9e5b-c7f3b33c00e1.png)

What went wrong? (add screenshot)
Does not show symbol
![image](https://user-images.githubusercontent.com/50500976/123409707-274cad00-d5b7-11eb-9a64-b11dcf3cdc3f.png)
Link to a viewer (if hosted on a site other than mozilla.github.io/pdf.js or as Firefox/Chrome extension): Latest Version Chrome extension

let glyphs = this._charsCache[chars];
    if (glyphs) {
      return glyphs;
    }
    glyphs = [];
    if (this.cMap) {
      
      
      const c = Object.create(null),
        ii = chars.length;
      let i = 0;
      while (i < ii) {
        this.cMap.readCharCode(chars, i, c);
        const { charcode, length } = c;
        i += length;
        
        const glyph = this._charToGlyph(
          charcode,
          length === 1 && chars.charCodeAt(i - 1) === 0x20
        );
        glyphs.push(glyph);
      }
    } else {
      for (let i = 0, ii = chars.length; i < ii; ++i) {
        const charcode = chars.charCodeAt(i);
        const glyph = this._charToGlyph(charcode, charcode === 0x20);
        glyphs.push(glyph);
      }