CBQE-0: fix negative unnest test

Change-Id: Ib792ac2b0e7e3ac98c50858e7c97d878840adb32
Reviewed-on: http://review.couchbase.org/32992
Reviewed-by: Iryna Mironava <irynamironava@yandex.ru>
Tested-by: Iryna Mironava <irynamironava@yandex.ru>