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):

warn("cmap table has unsupported format: " + format);
        return {
          platformId: -1,
          encodingId: -1,
          mappings: [],
          hasShortCmap: false,
        };
      }
      
      mappings.sort(function (a, b) {
        return a.charCode - b.charCode;
      });
      for (let i = 1; i < mappings.length; i++) {
        if (mappings[i - 1].charCode === mappings[i].charCode) {
          mappings.splice(i, 1);
          i--;
        }
      }
      return {
        platformId: potentialTable.platformId,
        encodingId: potentialTable.encodingId,
        mappings,
        hasShortCmap,
      };
    }
    function sanitizeMetrics(
      file,
      header,
      metrics,
      headTable,