Don't sort batches when there are no changes.

On node removal we change the batch, but don't set rebuild
as everything else should be drawn as is. A sort after such a removal
could result on the order of batches being changed without the other
nodes being updated. This would then result in incorrect ordering
and nodes could be obscured.

Task-number: QTBUG-37222

Change-Id: I57dd2fbc945e8c10c949743f59315b3372a4b6f4
Reviewed-by: Michael Brasser <michael.brasser@live.com>