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 

const possibleSpaceReplacements = ["space", "minus", "one", "i", "I"];
    let width;
    for (let i = 0, ii = possibleSpaceReplacements.length; i < ii; i++) {
      const glyphName = possibleSpaceReplacements[i];
      
      if (glyphName in this.widths) {
        width = this.widths[glyphName];
        break;
      }
      const glyphsUnicodeMap = getGlyphsUnicode();
      const glyphUnicode = glyphsUnicodeMap[glyphName];
      
      let charcode = 0;
      if (this.composite && this.cMap.contains(glyphUnicode)) {
        charcode = this.cMap.lookup(glyphUnicode);
      }
      
      if (!charcode && this.toUnicode) {
        charcode = this.toUnicode.charCodeOf(glyphUnicode);
      }
      
      if (charcode <= 0) {
        charcode = glyphUnicode;
      }
      
      width = this.widths[charcode];
      if (width) {
        break; 
      }