### 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
Dictionary floating_docks_dump = p_layout->get_value(p_section, "dock_floating", Dictionary());
	bool restore_window_on_load = EDITOR_GET("interface/multi_window/restore_windows_on_load");
	for (int i = 0; i < DOCK_SLOT_MAX; i++) {
		if (!p_layout->has_section_key(p_section, "dock_" + itos(i + 1))) {
			continue;
		}
		Vector<String> names = String(p_layout->get_value(p_section, "dock_" + itos(i + 1))).split(",");
		for (int j = names.size() - 1; j >= 0; j--) {
			String name = names[j];
			
			int atidx = -1;
			Control *node = nullptr;
			for (int k = 0; k < DOCK_SLOT_MAX; k++) {
				if (!dock_slot[k]->has_node(name)) {
					continue;
				}
				node = Object::cast_to<Control>(dock_slot[k]->get_node(name));
				if (!node) {
					continue;
				}
				atidx = k;
				break;