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 toFontChar = [];
  let unicode;
  for (let i = 0, ii = encoding.length; i < ii; i++) {
    unicode = getUnicodeForGlyph(encoding[i], glyphsUnicodeMap);
    if (unicode !== -1) {
      toFontChar[i] = unicode;
    }
  }
  for (const charCode in differences) {
    unicode = getUnicodeForGlyph(differences[charCode], glyphsUnicodeMap);
    if (unicode !== -1) {
      toFontChar[+charCode] = unicode;
    }
  }
  return toFontChar;
}
/**
 * Rebuilds the char code to glyph ID map by moving all char codes to the
 * private use area. This is done to avoid issues with various problematic
 * unicode areas where either a glyph won't be drawn or is deformed by a
 * shaper.
 * @returns {Object} Two properties:
 * 'toFontChar' - maps original char codes(the value that will be read
 * from commands such as show text) to the char codes that will be used in the
 * font that we build
 * 'charCodeToGlyphId' - maps the new font char codes to glyph ids
 */
function adjustMapping(charCodeToGlyphId, hasGlyph, newGlyphZeroId) {