Do not let the Fullscreen/Normal be completely unselected

If you choosed View->Fullscreen, the app would go to fullscreen,
but if you then go again to View->Fullscreen, the app would still
be fullscreen but the menu item would be unselected - leaving
UI and settings inconsistent.

Signed-off-by: Tomaz Canabrava <tomaz.canabrava@intel.com>