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

segment = segments[segIndex];
          start = segment.start;
          const end = segment.end;
          const delta = segment.delta;
          offsetIndex = segment.offsetIndex;
          for (j = start; j <= end; j++) {
            if (j === 0xffff) {
              continue;
            }
            glyphId = offsetIndex < 0 ? j : offsets[offsetIndex + j - start];
            glyphId = (glyphId + delta) & 0xffff;
            mappings.push({
              charCode: j,
              glyphId,
            });
          }
        }
      } else if (format === 6) {
        
        
        
        
        
        const firstCode = file.getUint16();
        const entryCount = file.getUint16();
        for (j = 0; j < entryCount; j++) {
          glyphId = file.getUint16();
          const charCode = firstCode + j;
          mappings.push({
            charCode,