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)



}
      tmpCanvas = this.cachedCanvases.getCanvas(
        tmpCanvasId,
        newWidth,
        newHeight
      );
      tmpCtx = tmpCanvas.context;
      tmpCtx.clearRect(0, 0, newWidth, newHeight);
      tmpCtx.drawImage(
        img,
        0,
        0,
        paintWidth,
        paintHeight,
        0,
        0,
        newWidth,
        newHeight
      );
      img = tmpCanvas.canvas;
      paintWidth = newWidth;
      paintHeight = newHeight;
      tmpCanvasId = tmpCanvasId === "prescale1" ? "prescale2" : "prescale1";
    }
    return {
      img,
      paintWidth,
      paintHeight,
    };
  }