Fix for issue #285.

This change closes a leaked Cursor after sharing an image to TweetLanes and helps correct issue #285. 
There was also a mismatched id, [as you can see here](https://github.com/adneal/TweetLanes/compare/chrislacy:develop...sharefix#L0R167) and I improved the `mLaneFragmentHashMap` performance by switching to a `SpareArray`.