### 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
tab_preview_panel->hide();
	if (p_tab == editor_data.get_edited_scene()) {
		return; 
	}
	set_current_scene(p_tab);
}
Button *EditorNode::add_bottom_panel_item(String p_text, Control *p_item) {
	Button *tb = memnew(Button);
	tb->set_flat(true);
	tb->connect("toggled", callable_mp(this, &EditorNode::_bottom_panel_switch).bind(bottom_panel_items.size()));
	tb->set_text(p_text);
	tb->set_toggle_mode(true);
	tb->set_focus_mode(Control::FOCUS_NONE);
	bottom_panel_vb->add_child(p_item);
	bottom_panel_hb->move_to_front();
	bottom_panel_hb_editors->add_child(tb);
	p_item->set_v_size_flags(Control::SIZE_EXPAND_FILL);
	p_item->hide();
	BottomPanelItem bpi;
	bpi.button = tb;
	bpi.control = p_item;
	bpi.name = p_text;
	bottom_panel_items.push_back(bpi);
	return tb;
}
void EditorNode::hide_bottom_panel() {