CBD-681: Return original tree when not adding items

When no new items get added to the tree, just return the
original tree.

Change-Id: I41a333183e6b189b0188e792f86b42c9f1ab4aea
Reviewed-on: http://review.couchbase.org/22984
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Filipe David Borba Manana <fdmanana@gmail.com>