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):

}
    
    return (this._charsCache[chars] = glyphs);
  }
  /**
   * Chars can have different sizes (depends on the encoding).
   * @param {String} a string encoded with font encoding.
   * @returns {Array<Array<number>>} the positions of each char in the string.
   */
  getCharPositions(chars) {
    
    
    const positions = [];
    if (this.cMap) {
      const c = Object.create(null);
      let i = 0;
      while (i < chars.length) {
        this.cMap.readCharCode(chars, i, c);
        const length = c.length;
        positions.push([i, i + length]);
        i += length;
      }
    } else {
      for (let i = 0, ii = chars.length; i < ii; ++i) {
        positions.push([i, i + 1]);
      }
    }
    return positions;
  }
  get glyphCacheValues() {