Bug Fix: PropertyHelper::stringToImage was not handling empty string case.
Bug Fix: PropertyHelper::stringToImage was not handling empty string case.

cbeck88/cegui-mirror,cbeck88/cegui-mirror,arkana-fts/cegui,RealityFactory/CEGUI,RealityFactory/CEGUI,cbeck88/cegui-mirror,arkana-fts/cegui,cbeck88/cegui-mirror,RealityFactory/CEGUI,RealityFactory/CEGUI,arkana-fts/cegui,RealityFactory/CEGUI,arkana-fts/cegui,cbeck88/cegui-mirror,arkana-fts/cegui