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):

const format = file.getUint16();
      file.skip(2 + 2); 
      let hasShortCmap = false;
      const mappings = [];
      let j, glyphId;
      
      if (format === 0) {
        for (j = 0; j < 256; j++) {
          const index = file.getByte();
          if (!index) {
            continue;
          }
          mappings.push({
            charCode: j,
            glyphId: index,
          });
        }
        hasShortCmap = true;
      } else if (format === 4) {
        
        
        const segCount = file.getUint16() >> 1;
        file.skip(6); 
        const segments = [];
        let segIndex;
        for (segIndex = 0; segIndex < segCount; segIndex++) {
          segments.push({ end: file.getUint16() });
        }
        file.skip(2);
        for (segIndex = 0; segIndex < segCount; segIndex++) {