site admins shouldn't see Space Stylesheet in the Space Admin menu if Space Stylesheets are turned off

If Enable Custom Stylesheets for Spaces is off (the default) then no one should see the space style sheet page or to edit space sytlesheets. Currently that's true for space admins but not for site admins. If it's deemed that site admin should see and edit the space stylesheets then there should be big warnings on the space sytlesheet page warning folks that the sytlesheet has no effect because space stylesheets are disabled.