### 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
switch (p_what) {
		case NOTIFICATION_PROCESS: {
			if (opening_prev && !confirmation->is_visible()) {
				opening_prev = false;
			}
			bool global_unsaved = EditorUndoRedoManager::get_singleton()->is_history_unsaved(EditorUndoRedoManager::GLOBAL_HISTORY);
			bool scene_or_global_unsaved = global_unsaved || EditorUndoRedoManager::get_singleton()->is_history_unsaved(editor_data.get_current_edited_scene_history_id());
			if (unsaved_cache != scene_or_global_unsaved) {
				unsaved_cache = scene_or_global_unsaved;
				_update_title();
			}
			if (editor_data.is_scene_changed(-1)) {
				_update_scene_tabs();
			}
			
			uint64_t frame = Engine::get_singleton()->get_frames_drawn();
			uint64_t tick = OS::get_singleton()->get_ticks_msec();
			if (frame != update_spinner_step_frame && (tick - update_spinner_step_msec) > (1000 / 8)) {
				update_spinner_step++;