MB-7435: Make sure chk_items always gets a value

Change-Id: I2fae9d8133e9fe794170b786b5629d061ade7456
Reviewed-on: http://review.couchbase.org/25922
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Reviewed-by: Jin Lim <jin@couchbase.com>