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):

toUnicode[charCode] = String.fromCharCode(unicode);
    }
  }
  if (toUnicode.length > 0) {
    properties.toUnicode.amend(toUnicode);
  }
}
/**
 * NOTE: This function should only be called at the *end* of font-parsing,
 *       after e.g. `adjustToUnicode` has run, to prevent any issues.
 */
function amendFallbackToUnicode(properties) {
  if (!properties.fallbackToUnicode) {
    return;
  }
  if (properties.toUnicode instanceof IdentityToUnicodeMap) {
    return;
  }
  const toUnicode = [];
  for (const charCode in properties.fallbackToUnicode) {
    if (properties.toUnicode.has(charCode)) {
      continue; 
    }
    toUnicode[charCode] = properties.fallbackToUnicode[charCode];
  }
  if (toUnicode.length > 0) {
    properties.toUnicode.amend(toUnicode);
  }
}
class Glyph {