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 

}
    width = width || this.defaultWidth;
    return shadow(this, "spaceWidth", width);
  }
  /**
   * @private
   */
  _charToGlyph(charcode, isSpace = false) {
    let fontCharCode, width, operatorListId;
    let widthCode = charcode;
    if (this.cMap && this.cMap.contains(charcode)) {
      widthCode = this.cMap.lookup(charcode);
    }
    width = this.widths[widthCode];
    width = isNum(width) ? width : this.defaultWidth;
    const vmetric = this.vmetrics && this.vmetrics[widthCode];
    let unicode = this.toUnicode.get(charcode) || charcode;
    if (typeof unicode === "number") {
      unicode = String.fromCharCode(unicode);
    }
    let isInFont = this.toFontChar[charcode] !== undefined;
    
    
    fontCharCode = this.toFontChar[charcode] || charcode;
    if (this.missingFile) {
      const glyphName =
        this.differences[charcode] || this.defaultEncoding[charcode];
      if (
        (glyphName === ".notdef" || glyphName === "") &&
        this.type === "Type1"