### 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_editor->has_main_screen()) {
		Button *tb = memnew(Button);
		tb->set_flat(true);
		tb->set_toggle_mode(true);
		tb->connect("pressed", callable_mp(singleton, &EditorNode::editor_select).bind(singleton->main_editor_buttons.size()));
		tb->set_name(p_editor->get_name());
		tb->set_text(p_editor->get_name());
		Ref<Texture2D> icon = p_editor->get_icon();
		if (icon.is_valid()) {
			tb->set_icon(icon);
			
			icon->connect("changed", callable_mp((Control *)tb, &Control::update_minimum_size));
		} else if (singleton->gui_base->has_theme_icon(p_editor->get_name(), SNAME("EditorIcons"))) {
			tb->set_icon(singleton->gui_base->get_theme_icon(p_editor->get_name(), SNAME("EditorIcons")));
		}
		tb->add_theme_font_override("font", singleton->gui_base->get_theme_font(SNAME("main_button_font"), SNAME("EditorFonts")));
		tb->add_theme_font_size_override("font_size", singleton->gui_base->get_theme_font_size(SNAME("main_button_font_size"), SNAME("EditorFonts")));
		singleton->main_editor_buttons.push_back(tb);
		singleton->main_editor_button_hb->add_child(tb);
		singleton->editor_table.push_back(p_editor);
		singleton->distraction_free->move_to_front();
	}
	singleton->editor_data.add_editor_plugin(p_editor);
	singleton->add_child(p_editor);
	if (p_config_changed) {
		p_editor->enable_plugin();
	}
}
void EditorNode::remove_editor_plugin(EditorPlugin *p_editor, bool p_config_changed) {