Fix off-by-one error in TransclusionModel when moving items

The error occurs when moving an item down (increasing index) which
removes the item, adjusts the index and then inserts the item. The index
shouldn't be adjusted when moving one down, however, because once
removed everything shifts and the +1 index set initially to move it is
still good.

Change-Id: I44bd2b3eb4bbbef58a6ac181e75969ec7c2cab6f