Rows are disappearing when thrown

I am using the [given example](https://github.com/deanmcpherson/react-native-sortable-listview/blob/master/example.js) to demonstrate this bug. If you drag an item and throw it off screen then if will disappear and weirdly format the SortableListView.

This is what I mean: http://www.giphy.com/gifs/3o752enWLnM5uZgYCc

Start with the given example in example.js and run the React Native demonstration. Reproduce the issue by dragging an item off screen, then inspect how SortableListView behaves after the item disappears. Done means throwing an item off screen no longer makes the list disappear or become incorrectly formatted.

Written by the indexing model from the issue text.