Add nullcheck for iostream before close

Loading images in a RecyclerView using the beta PixelFetcher:

    PixelFetchers.getInstance(context).load(show.getPosterUrl(), posterImageView);

![screen shot 2014-12-30 at 08 39 11](https://cloud.githubusercontent.com/assets/2678555/5576976/62c335e8-8fff-11e4-9bda-5388618c86f2.png)

On attempting to scroll through the list, the app crashes with NPE in UrlNetworkManager.