While we normally try to avoid whitespace fixes, the gtk-demo code is shown as exemplary, so it should be in good shape, formatting-wise.
Because it's FALSE in virtually all use cases.
Use gtk_widget_get_visible() instead https://bugzilla.gnome.org/show_bug.cgi?id=69872
Signed-off-by: David Zeuthen <davidz@redhat.com>