Link to PDF file (or attach file here):
Document is copyright protected


Configuration:
- Web browser and its version: Chrome 54.0.2840.71
- Operating system and its version: Windows 7 Build 7061
- PDF.js version: 1.7.225
- Is an extension: no

Steps to reproduce the problem:
1. Load file in pdf.js
2. View thumbnails

What is the expected behavior? (add screenshot)

It works fine in OS X (though image downsampling looks better on the first two pages) :

![mac](https://cloud.githubusercontent.com/assets/5866973/24648555/41bb5df2-1924-11e7-8d94-22ed2972fb0a.png)

What went wrong? (add screenshot)

In Windows the first thumbnails (the pages that have been rendered in full view) are fine. The following thumbnails which are not rendered in full view look like the downsampling didnt work.

![screen shot 2017-04-04 at 10 41 02](https://cloud.githubusercontent.com/assets/5866973/24648675/a826d95e-1924-11e7-928a-c64a16dec7a8.png)

![screen shot 2017-04-04 at 10 41 20](https://cloud.githubusercontent.com/assets/5866973/24648870/608810ee-1925-11e7-8f4c-b0d51c54a9c8.png)


Link to a viewer (if hosted on a site other than mozilla.github.io/pdf.js or as Firefox/Chrome extension): https://mozilla.github.io/pdf.js/web/viewer.html
const tempCanvas = tempCanvasCache;
      if (tempCanvas) {
        
        
        tempCanvas.width = 0;
        tempCanvas.height = 0;
      }
      tempCanvasCache = null;
    },
  };
})();
/**
 * @implements {IRenderableView}
 */
class PDFThumbnailView {
  /**
   * @param {PDFThumbnailViewOptions} options
   */
  constructor({
    container,
    id,
    defaultViewport,
    optionalContentConfigPromise,
    linkService,
    renderingQueue,
    checkSetImageDisabled,
    disableCanvasToImageConversion = false,