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).
scaleX: dimx.scale,
        scaleY: dimy.scale,
      };
    },
    getSizeAndScale: function TilingPattern_getSizeAndScale(
      step,
      realOutputSize,
      scale
    ) {
      
      step = Math.abs(step);
      
      
      
      
      const maxSize = Math.max(MAX_PATTERN_SIZE, realOutputSize);
      let size = Math.ceil(step * scale);
      if (size >= maxSize) {
        size = maxSize;
      } else {
        scale = size / step;
      }
      return { scale, size };
    },
    clipBbox: function clipBbox(graphics, bbox, x0, y0, x1, y1) {
      if (Array.isArray(bbox) && bbox.length === 4) {
        const bboxWidth = x1 - x0;
        const bboxHeight = y1 - y0;
        graphics.ctx.rect(x0, y0, bboxWidth, bboxHeight);
        graphics.clip();