Link to PDF file (or attach file here):
[RP_25884_V2_UEL Semi Finals 2016-17_concepts.pdf](https://github.com/mozilla/pdf.js/files/994423/RP_25884_V2_UEL.Semi.Finals.2016-17_concepts.pdf)

Configuration:
- Web browser and its version: Chrome 58, Firefox 53
- Operating system and its version: MacOS 10.11.6
- PDF.js version:
- Is an extension: No

Steps to reproduce the problem:
1.  View the file the file


What is the expected behavior? (add screenshot)
<img width="560" alt="screen shot 2017-05-11 at 2 06 36 pm" src="https://cloud.githubusercontent.com/assets/2474027/25971992/189f4ebe-3653-11e7-8847-c9011984cb8d.png">

What went wrong? (add screenshot)
Textlayer exists here but font fails to render. No warning in the console from what I can see. Maybe related to the gradient?

<img width="637" alt="screen shot 2017-05-11 at 2 06 20 pm" src="https://cloud.githubusercontent.com/assets/2474027/25971997/1b518cc6-3653-11e7-96c0-9a03ffcb7d6e.png">

Thanks!
j0 = i * width1;
    if (data[pos - lineSize] !== data[pos]) {
      points[j0] = data[pos] ? 1 : 8;
      ++count;
    }
    
    
    let sum = (data[pos] ? 4 : 0) + (data[pos - lineSize] ? 8 : 0);
    for (j = 1; j < width; j++) {
      sum =
        (sum >> 2) +
        (data[pos + 1] ? 4 : 0) +
        (data[pos - lineSize + 1] ? 8 : 0);
      if (POINT_TYPES[sum]) {
        points[j0 + j] = POINT_TYPES[sum];
        ++count;
      }
      pos++;
    }
    if (data[pos - lineSize] !== data[pos]) {
      points[j0 + j] = data[pos] ? 2 : 4;
      ++count;
    }
    if (count > POINT_TO_PROCESS_LIMIT) {
      return null;
    }
  }
  pos = lineSize * (height - 1);
  j0 = i * width1;
  if (data[pos] !== 0) {