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 possibleSpaceReplacements = ["space", "minus", "one", "i", "I"];
    let width;
    for (let i = 0, ii = possibleSpaceReplacements.length; i < ii; i++) {
      const glyphName = possibleSpaceReplacements[i];
      
      if (glyphName in this.widths) {
        width = this.widths[glyphName];
        break;
      }
      const glyphsUnicodeMap = getGlyphsUnicode();
      const glyphUnicode = glyphsUnicodeMap[glyphName];
      
      let charcode = 0;
      if (this.composite && this.cMap.contains(glyphUnicode)) {
        charcode = this.cMap.lookup(glyphUnicode);
      }
      
      if (!charcode && this.toUnicode) {
        charcode = this.toUnicode.charCodeOf(glyphUnicode);
      }
      
      if (charcode <= 0) {
        charcode = glyphUnicode;
      }
      
      width = this.widths[charcode];
      if (width) {
        break; 
      }