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!
maskCtx,
  layerCtx,
  width,
  height,
  subtype,
  backdrop,
  transferMap
) {
  const hasBackdrop = !!backdrop;
  const r0 = hasBackdrop ? backdrop[0] : 0;
  const g0 = hasBackdrop ? backdrop[1] : 0;
  const b0 = hasBackdrop ? backdrop[2] : 0;
  let composeFn;
  if (subtype === "Luminosity") {
    composeFn = composeSMaskLuminosity;
  } else {
    composeFn = composeSMaskAlpha;
  }
  
  const PIXELS_TO_PROCESS = 1048576;
  const chunkSize = Math.min(height, Math.ceil(PIXELS_TO_PROCESS / width));
  for (let row = 0; row < height; row += chunkSize) {
    const chunkHeight = Math.min(chunkSize, height - row);
    const maskData = maskCtx.getImageData(0, row, width, chunkHeight);
    const layerData = layerCtx.getImageData(0, row, width, chunkHeight);