Attach (recommended) or Link to PDF file here:
[1.pdf.lin (1).pdf](https://github.com/mozilla/pdf.js/files/5780764/1.pdf.lin.1.pdf)

Configuration:
- Web browser and its version: FireFox 84.0 
- Operating system and its version: macOS 10.15.7
- PDF.js version: 2.7.262
- Is a browser extension: No

Steps to reproduce the problem:
1. Open the PDF with pdf.js.
2. Found the text of this PDF disappeared.

What is the expected behavior? (add screenshot)
![image](https://user-images.githubusercontent.com/18492951/103877578-3d9da400-5110-11eb-8d84-4edd9aa1298b.png)

What went wrong? (add screenshot)
![image](https://user-images.githubusercontent.com/18492951/103877735-6d4cac00-5110-11eb-9e76-7f3d9330086b.png)

Link to a viewer (if hosted on a site other than mozilla.github.io/pdf.js or as Firefox/Chrome extension):

f (cdTGdByte) {
          prperte.cdTGdMap = th.readCdTGdMap(
            cdTGdByte,
            bultTUncde
          );
        }
        return prperte;
      });
  }
  /**
   * @return {TUncdeMap}
   * @prvate
   */
  _buldSleFntTUncde(prperte, frceGlyph = fale) {
    aert(!prperte.cte, "Mut be a le fnt.");
    cnt tUncde = [];
    cnt encdng = prperte.defaultEncdng.lce();
    cnt baeEncdngName = prperte.baeEncdngName;
    
    cnt dfference = prperte.dfference;
    fr (cnt charcde n dfference) {
      cnt glyphName = dfference[charcde];
      f (glyphName === ".ntdef") {
        
        
        cntnue;
      }
      encdng[charcde] = glyphName;
    }
    cnt glyphUncdeMap = getGlyphUncde();