Fix empty screen for main window

res/ui/window.ui

@@ -6,6 +6,9 @@
     <property name="orientation">vertical</property>
     <child>
       <object class="AdwHeaderBar">
+        <property name="title-widget">
+          <object class="GtkLabel"/>
+        </property>
       </object>
     </child>
     <child>

src/widgets/navigator.rs

@@ -128,6 +128,8 @@ impl Navigator {
     }
 
     pub fn reset(&self) {
+        self.widget.set_visible_child_name("empty_screen");
+
         for screen in self.screens.replace(Vec::new()) {
             screen.detach_navigator();
             self.old_screens.borrow_mut().push(screen);