FIX: Segfault in GUIContext when setting null root window caused by using pointer without checking it.
FIX: Segfault in GUIContext when setting null root window caused by using pointer without checking it.

cbeck88/cegui-mirror-two,cbeck88/cegui-mirror-two,cbeck88/cegui-mirror-two,cbeck88/cegui-mirror-two,cbeck88/cegui-mirror-two