Attach (recommended) or Link to PDF file here:
[双引号不正常.pdf](https://github.com/mozilla/pdf.js/files/3533108/default.pdf)


Configuration:
- Web browser and its version:  IE11 , chrome 
- Operating system and its version:  win7
- PDF.js version:  master
- Is a browser extension: nothing 
teps to reproduce the problem:
1. viewer.html web  online preview


What is the expected behavior? (add screenshot)
Displayed in normal characters.

What went wrong? (add screenshot)
![20190823143813](https://user-images.githubusercontent.com/6269307/63571860-062e6600-c5b4-11e9-9fff-75d65cf6bade.png)

Not only the two characters I took screenshots, but also a lot of garbled Chinese punctuation. For example, the Chinese 《》 symbol. But these garbled characters only appear in some specific very old pdf files.

Link to a viewer (if hosted on a site other than mozilla.github.io/pdf.js or as Firefox/Chrome extension):nothing 

mappings: [],
          hasShortCmap: false,
        };
      }
      let segment;
      let start = (file.start ? file.start : 0) + cmap.offset;
      file.pos = start;
      file.skip(2); 
      const numTables = file.getUint16();
      let potentialTable;
      let canBreak = false;
      
      
      
      
      
      
      for (let i = 0; i < numTables; i++) {
        const platformId = file.getUint16();
        const encodingId = file.getUint16();
        const offset = file.getInt32() >>> 0;
        let useTable = false;
        
        
        if (
          potentialTable &&
          potentialTable.platformId === platformId &&
          potentialTable.encodingId === encodingId
        ) {
          continue;