### 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
for (int i = 0; i < DOCK_SLOT_MAX; i++) {
		String names;
		for (int j = 0; j < dock_slot[i]->get_tab_count(); j++) {
			String name = dock_slot[i]->get_tab_control(j)->get_name();
			if (!names.is_empty()) {
				names += ",";
			}
			names += name;
		}
		String config_key = "dock_" + itos(i + 1);
		if (p_layout->has_section_key(p_section, config_key)) {
			p_layout->erase_section_key(p_section, config_key);
		}
		if (!names.is_empty()) {
			p_layout->set_value(p_section, config_key, names);
		}
		int selected_tab_idx = dock_slot[i]->get_current_tab();