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):

const unitsPerEm =
    override.unitsPerEm ||
    1 / (properties.fontMatrix || FONT_IDENTITY_MATRIX)[0];
  
  
  const scale = properties.ascentScaled
    ? 1.0
    : unitsPerEm / PDF_GLYPH_SPACE_UNITS;
  const typoAscent =
    override.ascent || Math.round(scale * (properties.ascent || bbox[3]));
  let typoDescent =
    override.descent || Math.round(scale * (properties.descent || bbox[1]));
  if (typoDescent > 0 && properties.descent > 0 && bbox[1] < 0) {
    typoDescent = -typoDescent; 
  }
  const winAscent = override.yMax || typoAscent;
  const winDescent = -override.yMin || -typoDescent;
  return (
    "\x00\x03" + 
    "\x02\x24" + 
    "\x01\xF4" + 
    "\x00\x05" + 
    "\x00\x00" + 
    "\x02\x8A" + 
    "\x02\xBB" + 
    "\x00\x00" + 
    "\x00\x8C" + 
    "\x02\x8A" + 
    "\x02\xBB" + 
    "\x00\x00" +