QuickShow: Hide toolbar container in fullscreen mode

If we just hide the toolbar itself, its container is still visible and
taking up space at the top of the screen.

Applications/QuickShow/main.cpp

@@ -193,7 +193,7 @@ int main(int argc, char** argv)
     auto full_sceen_action = GUI::CommonActions::make_fullscreen_action(
         [&](auto&) {
             window->set_fullscreen(!window->is_fullscreen());
-            main_toolbar.set_visible(!window->is_fullscreen());
+            toolbar_container.set_visible(!window->is_fullscreen());
         });
 
     auto zoom_in_action = GUI::Action::create("Zoom In", { Mod_None, Key_Plus }, Gfx::Bitmap::load_from_file("/res/icons/16x16/zoom-in.png"),