Fixed bug of sending empty child attribute at Scene List Resource response.

Fixed bug of sending empty child attribute at Scene List Resource response.

If Scene resource has not children, these attribute's value is empty.
But CBOR parser can not parsing empty attribute.
This patch, attribute remove when the attribute's value is empty.

Change-Id: Iaa0be2cf0df19211b2b2598ec47da94286068e4c
Signed-off-by: jyong2.kim <jyong2.kim@samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/5215
Reviewed-by: Uze Choi <uzchoi@samsung.com>
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>