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 

font.skip(28);
      let glyphNames;
      let valid = true;
      let i;
      switch (version) {
        case 0x00010000:
          glyphNames = MacStandardGlyphOrdering;
          break;
        case 0x00020000:
          const numGlyphs = font.getUint16();
          if (numGlyphs !== maxpNumGlyphs) {
            valid = false;
            break;
          }
          const glyphNameIndexes = [];
          for (i = 0; i < numGlyphs; ++i) {
            const index = font.getUint16();
            if (index >= 32768) {
              valid = false;
              break;
            }
            glyphNameIndexes.push(index);
          }
          if (!valid) {
            break;
          }
          const customNames = [],
            strBuf = [];
          while (font.pos < end) {
            const stringLength = font.getByte();