popover: Apply settings enabled stateto UI

src/popover.rs

@@ -364,6 +364,7 @@ pub fn show(
     };
 
     let settings_action = gio::SimpleAction::new("settings", None);
+    settings_action.set_enabled(popover.settings_active);
     settings_action.connect_activate(move |_, _| {
         let s = CString::new("region").unwrap();
         unsafe { c::popover_open_settings_panel(s.as_ptr()) };