### 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
if (p_config_file->has_section_key(EDITOR_NODE_CONFIG_SECTION, "center_split_offset")) {
		int center_split_offset = p_config_file->get_value(EDITOR_NODE_CONFIG_SECTION, "center_split_offset");
		center_split->set_split_offset(center_split_offset);
	}
	if (p_config_file->has_section_key(EDITOR_NODE_CONFIG_SECTION, "selected_bottom_panel_item")) {
		int selected_bottom_panel_item_idx = p_config_file->get_value(EDITOR_NODE_CONFIG_SECTION, "selected_bottom_panel_item");
		if (selected_bottom_panel_item_idx >= 0 && selected_bottom_panel_item_idx < bottom_panel_items.size()) {
			
			if (bottom_panel_items[selected_bottom_panel_item_idx].button->is_visible()) {
				_bottom_panel_switch(true, selected_bottom_panel_item_idx);
			}
		}
	}
	
	if (p_config_file->has_section_key(EDITOR_NODE_CONFIG_SECTION, "selected_default_debugger_tab_idx")) {
		int selected_default_debugger_tab_idx = p_config_file->get_value(EDITOR_NODE_CONFIG_SECTION, "selected_default_debugger_tab_idx");
		EditorDebuggerNode::get_singleton()->get_default_debugger()->switch_to_debugger(selected_default_debugger_tab_idx);
	}
	
	if (p_config_file->has_section_key(EDITOR_NODE_CONFIG_SECTION, "selected_main_editor_idx")) {
		int selected_main_editor_idx = p_config_file->get_value(EDITOR_NODE_CONFIG_SECTION, "selected_main_editor_idx");
		if (selected_main_editor_idx >= 0 && selected_main_editor_idx < main_editor_buttons.size()) {
			callable_mp(this, &EditorNode::editor_select).call_deferred(selected_main_editor_idx);
		}
	}
}
void EditorNode::_load_open_scenes_from_config(Ref<ConfigFile> p_layout) {