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 metricsOverride = {
      unitsPerEm: int16(tables.head.data[18], tables.head.data[19]),
      yMax: int16(tables.head.data[42], tables.head.data[43]),
      yMin: signedInt16(tables.head.data[38], tables.head.data[39]),
      ascent: signedInt16(tables.hhea.data[4], tables.hhea.data[5]),
      descent: signedInt16(tables.hhea.data[6], tables.hhea.data[7]),
      lineGap: signedInt16(tables.hhea.data[8], tables.hhea.data[9]),
    };
    
    this.ascent = metricsOverride.ascent / metricsOverride.unitsPerEm;
    this.descent = metricsOverride.descent / metricsOverride.unitsPerEm;
    this.lineGap = metricsOverride.lineGap / metricsOverride.unitsPerEm;
    if (this.cssFontInfo && this.cssFontInfo.lineHeight) {
      this.lineHeight = this.cssFontInfo.metrics.lineHeight;
      this.lineGap = this.cssFontInfo.metrics.lineGap;
    } else {
      this.lineHeight = this.ascent - this.descent + this.lineGap;
    }
    
    if (tables.post) {
      readPostScriptTable(tables.post, properties, numGlyphs);
    }
    
    tables.post = {
      tag: "post",
      data: createPostTable(properties),
    };
    const charCodeToGlyphId = [];
    
    function hasGlyph(glyphId) {