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

}
      if (this.toUnicode) {
        const char = String.fromCodePoint(unicode);
        const charCode = this.toUnicode.charCodeOf(char);
        if (charCode !== -1) {
          if (hasCurrentBufErrors()) {
            buffers.push(currentBuf.join(""));
            currentBuf.length = 0;
          }
          const charCodeLength = this.cMap
            ? this.cMap.getCharCodeLength(charCode)
            : 1;
          for (let j = charCodeLength - 1; j >= 0; j--) {
            currentBuf.push(String.fromCharCode((charCode >> (8 * j)) & 0xff));
          }
          continue;
        }
      }
      
      if (!hasCurrentBufErrors()) {
        buffers.push(currentBuf.join(""));
        currentBuf.length = 0;
      }
      currentBuf.push(String.fromCodePoint(unicode));
    }
    buffers.push(currentBuf.join(""));
    return buffers;
  }
}
class ErrorFont {