Link to PDF file (or attach file here):
[pages4.pdf](https://github.com/mozilla/pdf.js/files/1128300/pages4.pdf)

Configuration:
- Web browser and its version: Firefox 54
- Operating system and its version: Win 10
- PDF.js version: 1.8.522
- Is an extension: no

What is the expected behavior? (add screenshot)
![chrome1-1 1](https://user-images.githubusercontent.com/146436/27918380-2f74512a-6245-11e7-8525-d0038fa6c2e8.jpg)
![chrome1-2 1](https://user-images.githubusercontent.com/146436/27918425-54f8e47e-6245-11e7-9bff-127f79ad0511.jpg)


What went wrong? (add screenshot)
![screenshot from 2017-07-06 12-10-30](https://user-images.githubusercontent.com/146436/27918442-5d57624e-6245-11e7-9436-5ba31cc8bd1a.png)
![screenshot from 2017-07-06 12-10-44](https://user-images.githubusercontent.com/146436/27918454-63b486da-6245-11e7-9eb5-c03aa5c40943.png)



0,
      width,
      height
    );
    fillCtx.globalCompositeOperation = "source-in";
    const inverse = Util.transform(fillCtx.mozCurrentTransformInverse, [
      1,
      0,
      0,
      1,
      -offsetX,
      -offsetY,
    ]);
    fillCtx.fillStyle = isPatternFill
      ? fillColor.getPattern(ctx, this, inverse, false)
      : fillColor;
    fillCtx.fillRect(0, 0, width, height);
    
    return {
      canvas: fillCanvas.canvas,
      offsetX: Math.round(offsetX),
      offsetY: Math.round(offsetY),
    };
  }
  
  setLineWidth(width) {
    this.current.lineWidth = width;
    this.ctx.lineWidth = width;
  }
  setLineCap(style) {