Unregist visual directly when IMAGE have empty map

Unregist visual directly when IMAGE have empty map

Directly unregist visual when Property::IMAGE have empty map.
This code just follow up the action of control's Property::BACKGROUND doing.

When map is empty, the visual cannot be created. So it will always unregist visual before.
This patch just unregist the IMAGE's visual directly.
This will not print error message when NUI try to Unregist imagevisual

Change-Id: Ifdabbf3555a4471b0d3cf1da7b3f405a5e91553b
Signed-off-by: Eunki, Hong <eunkiki.hong@samsung.com>