N1QL skip generation of items if there was no load

Change-Id: I2af199e3deddc813e13fa8d5f466a1330342782d
Reviewed-on: http://review.couchbase.org/43914
Reviewed-by: Iryna Mironava <irynamironava@yandex.ru>
Tested-by: Iryna Mironava <irynamironava@yandex.ru>