Link to PDF file (or attach file here):
[gradient invisible pdfjs.pdf](https://github.com/mozilla/pdf.js/files/1096729/gradient.invisible.pdfjs.pdf)

Configuration:
- Web browser and its version: 59.0.3071.109
- Operating system and its version: Windows 10
- PDF.js version: 1.8.480
- Is an extension: No

Steps to reproduce the problem:
1. Open the file in Adobe Reader or Google Chrome
2. Open the file in PDFjs online viewer
3. Compare

What is the expected behavior? (add screenshot)
- There is an orange radial gradient, from opacity 0 at the center to opacity 1 at the page bound

![image](https://user-images.githubusercontent.com/17966696/27466423-3923639e-57e3-11e7-841f-7f498732bb20.png)

What went wrong? (add screenshot)
- The gradient is completely missing

![image](https://user-images.githubusercontent.com/17966696/27466446-63e36606-57e3-11e7-86c3-9a5e0b6b0e0a.png)

Link to a viewer (if hosted on a site other than mozilla.github.io/pdf.js or as Firefox/Chrome extension):
http://mozilla.github.io/pdf.js/web/viewer.html

Description of the file:
An opaque orange gradient is masked with a mask. The mask's group contains a rectangle filled with a pattern. The pattern contains an other rectangle filled with a greyscale gradient from black to white. All the rectangles, patterns & groups have the same size as the page (400x400pt).
tmpCtx.fill();
        const pattern = ctx.createPattern(tmpCanvas.canvas, "repeat");
        pattern.setTransform(createMatrix(ctx.mozCurrentTransformInverse));
        return pattern;
      },
    };
  },
};
const createMeshCanvas = (function createMeshCanvasClosure() {
  function drawTriangle(data, context, p1, p2, p3, c1, c2, c3) {
    
    const coords = context.coords,
      colors = context.colors;
    const bytes = data.data,
      rowSize = data.width * 4;
    let tmp;
    if (coords[p1 + 1] > coords[p2 + 1]) {
      tmp = p1;
      p1 = p2;
      p2 = tmp;
      tmp = c1;
      c1 = c2;
      c2 = tmp;
    }
    if (coords[p2 + 1] > coords[p3 + 1]) {
      tmp = p2;
      p2 = p3;
      p3 = tmp;
      tmp = c2;
      c2 = c3;