### 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 (restore_window_on_load && floating_docks_dump.has(name)) {
				_restore_floating_dock(floating_docks_dump[name], node, i);
			} else if (wrapper) {
				_dock_floating_close_request(wrapper);
			}
		}
		if (!p_layout->has_section_key(p_section, "dock_" + itos(i + 1) + "_selected_tab_idx")) {
			continue;
		}
		int selected_tab_idx = p_layout->get_value(p_section, "dock_" + itos(i + 1) + "_selected_tab_idx");
		if (selected_tab_idx >= 0 && selected_tab_idx < dock_slot[i]->get_tab_count()) {
			dock_slot[i]->call_deferred("set_current_tab", selected_tab_idx);
		}
	}
	for (int i = 0; i < vsplits.size(); i++) {
		if (!p_layout->has_section_key(p_section, "dock_split_" + itos(i + 1))) {
			continue;
		}
		int ofs = p_layout->get_value(p_section, "dock_split_" + itos(i + 1));
		vsplits[i]->set_split_offset(ofs);
	}
	for (int i = 0; i < hsplits.size(); i++) {
		if (!p_layout->has_section_key(p_section, "dock_hsplit_" + itos(i + 1))) {
			continue;
		}
		int ofs = p_layout->get_value(p_section, "dock_hsplit_" + itos(i + 1));
		hsplits[i]->set_split_offset(ofs);
	}
	for (int i = 0; i < vsplits.size(); i++) {
		bool in_use = dock_slot[i * 2 + 0]->get_tab_count() || dock_slot[i * 2 + 1]->get_tab_count();