Attach (recommended) or Link to PDF file here:

Configuration:
- Web browser and its version: Chrome 63.0.3239.132 
- Operating system and its version: Windows 10
- PDF.js version: using your official demo project
- Is a browser extension: No

Steps to reproduce the problem:
1.  Just load attached pdf
2.

What is the expected behavior? (add screenshot)
[E-WG18_105147.pdf](https://github.com/mozilla/pdf.js/files/1634833/E-WG18_105147.pdf)

What went wrong? (add screenshot)
![image](https://user-images.githubusercontent.com/29802177/34986271-3ca71a5c-fab7-11e7-95e8-1739dda3cd04.png)

Link to a viewer (if hosted on a site other than mozilla.github.io/pdf.js or as Firefox/Chrome extension):

getGlyphsUnicode(),
        this.differences
      );
    } else if (/Dingbats/i.test(fontName)) {
      if (/Wingdings/i.test(name)) {
        warn("Non-embedded Wingdings font, falling back to ZapfDingbats.");
      }
      this.toFontChar = buildToFontChar(
        ZapfDingbatsEncoding,
        getDingbatsGlyphsUnicode(),
        this.differences
      );
    } else if (isStandardFont) {
      const map = buildToFontChar(
        this.defaultEncoding,
        getGlyphsUnicode(),
        this.differences
      );
      if (
        type === "CIDFontType2" &&
        !this.cidEncoding.startsWith("Identity-") &&
        !(this.toUnicode instanceof IdentityToUnicodeMap)
      ) {
        this.toUnicode.forEach(function (charCode, unicodeCharCode) {
          map[+charCode] = unicodeCharCode;
        });
      }
      this.toFontChar = map;
    } else {
      const glyphsUnicodeMap = getGlyphsUnicode();