Check the drop point is not a footer.

I think this patch addresses the crash caused from dropping an item on the footer when present.

     08-01 17:49:09.628  30242-30242/? E/MessageQueue-JNI: java.lang.ArrayIndexOutOfBoundsException: length=7; index=7
     at com.terlici.dragndroplist.DragNDropCursorAdapter.onItemDrop(DragNDropCursorAdapter.java:97)
     at com.terlici.dragndroplist.DragNDropListView.stopDrag(DragNDropListView.java:249)
     at com.terlici.dragndroplist.DragNDropListView.onTouchEvent(DragNDropListView.java:156)