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 accentGlyphName = StandardEncoding[seac[3]];
        const baseGlyphId = charset.indexOf(baseGlyphName);
        const accentGlyphId = charset.indexOf(accentGlyphName);
        if (baseGlyphId < 0 || accentGlyphId < 0) {
          continue;
        }
        const accentOffset = {
          x: seac[0] * matrix[0] + seac[1] * matrix[2] + matrix[4],
          y: seac[0] * matrix[1] + seac[1] * matrix[3] + matrix[5],
        };
        const charCodes = getCharCodes(mapping, glyphId);
        if (!charCodes) {
          
          
          continue;
        }
        for (let i = 0, ii = charCodes.length; i < ii; i++) {
          const charCode = charCodes[i];
          
          
          const charCodeToGlyphId = newMapping.charCodeToGlyphId;
          const baseFontCharCode = createCharCode(
            charCodeToGlyphId,
            baseGlyphId
          );
          const accentFontCharCode = createCharCode(
            charCodeToGlyphId,
            accentGlyphId
          );
          seacMap[charCode] = {