### 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
EditorPlugin::AfterGUIInput after = EditorPlugin::AFTER_GUI_INPUT_PASS;
	for (int i = 0; i < plugins_list.size(); i++) {
		if ((!serve_when_force_input_enabled) && plugins_list[i]->is_input_event_forwarding_always_enabled()) {
			continue;
		}
		EditorPlugin::AfterGUIInput current_after = plugins_list[i]->forward_3d_gui_input(p_camera, p_event);
		if (current_after == EditorPlugin::AFTER_GUI_INPUT_STOP) {
			after = EditorPlugin::AFTER_GUI_INPUT_STOP;
		}
		if (after != EditorPlugin::AFTER_GUI_INPUT_STOP && current_after == EditorPlugin::AFTER_GUI_INPUT_CUSTOM) {
			after = EditorPlugin::AFTER_GUI_INPUT_CUSTOM;
		}
	}
	return after;
}
void EditorPluginList::forward_canvas_draw_over_viewport(Control *p_overlay) {
	for (int i = 0; i < plugins_list.size(); i++) {
		plugins_list[i]->forward_canvas_draw_over_viewport(p_overlay);
	}
}
void EditorPluginList::forward_canvas_force_draw_over_viewport(Control *p_overlay) {
	for (int i = 0; i < plugins_list.size(); i++) {
		plugins_list[i]->forward_canvas_force_draw_over_viewport(p_overlay);
	}
}
void EditorPluginList::forward_3d_draw_over_viewport(Control *p_overlay) {