### 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 (!docks_visible) {
		for (int i = 0; i < DOCK_SLOT_MAX; i++) {
			dock_slot[i]->hide();
		}
		for (int i = 0; i < vsplits.size(); i++) {
			vsplits[i]->hide();
		}
		right_hsplit->hide();
	} else {
		for (int i = 0; i < DOCK_SLOT_MAX; i++) {
			int tabs_visible = 0;
			for (int j = 0; j < dock_slot[i]->get_tab_count(); j++) {
				if (!dock_slot[i]->is_tab_hidden(j)) {
					tabs_visible++;
				}