reduce redraw issues on screen change

fix crash when lvobj is already deleted, but events are still in the queue

radio/src/thirdparty/libopenui/src/button.cpp

@@ -28,6 +28,9 @@ void Button::onPress()
   if (check != bool(windowFlags & BUTTON_CHECKED)) {
     windowFlags ^= BUTTON_CHECKED;
 
+    if(lvobj == nullptr)
+      return;
+
     if (! (windowFlags & BUTTON_CHECKED))
       lv_obj_clear_state(lvobj, LV_STATE_CHECKED);
     else 

radio/src/thirdparty/libopenui/src/layer.h

@@ -47,9 +47,10 @@ class Layer
       }
 
       // layers are screens in lvgl
-      lv_scr_load(window->getLvObj());
       lv_obj_set_parent(canvas, window->getLvObj());
       lv_obj_move_background(canvas);
+      lv_scr_load(window->getLvObj());
+      lv_obj_invalidate(canvas);
 
       stack.emplace_back(Layer(window));