### Godot version

4.1 rc3

### System information

Windows 10.0.19045 - Vulkan (Forward+) - dedicated NVIDIA GeForce GTX 1060 (NVIDIA; 30.0.15.1403) - Intel(R) Core(TM) i7-7700HQ CPU @ 2.80GHz (8 Threads)

### Issue description

This™
![image](https://github.com/godotengine/godot/assets/2223172/cb33110f-a5b0-400a-951f-3fa425f05714)

It can still happen, but it's more difficult to trigger.

### Steps to reproduce

1. Create a new scene with a Control node
2. Add Theme to the Control
3. Open Theme Editor
4. Clear the `theme` property in Control
5. Save, with Theme Editor opened
6. Restart

### Minimal reproduction project

N/A
open_imported->hide();
	load_scene(open_import_request, true, true);
}
void EditorNode::_open_imported() {
	load_scene(open_import_request, true, false, true, true);
}
void EditorNode::dim_editor(bool p_dimming) {
	dimmed = p_dimming;
	gui_base->set_modulate(p_dimming ? Color(0.5, 0.5, 0.5) : Color(1, 1, 1));
}
bool EditorNode::is_editor_dimmed() const {
	return dimmed;
}
void EditorNode::open_export_template_manager() {
	export_template_manager->popup_manager();
}
void EditorNode::add_resource_conversion_plugin(const Ref<EditorResourceConversionPlugin> &p_plugin) {