### 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++) {
		if (dock_slot[i]->get_tab_count() == 0 && dock_slot[i]->is_visible()) {
			dock_slot[i]->hide();
		}
		if (dock_slot[i]->get_tab_count() > 0 && !dock_slot[i]->is_visible()) {
			dock_slot[i]->show();
		}
	}
	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();
		if (in_use) {
			vsplits[i]->show();
		} else {
			vsplits[i]->hide();
		}
	}
	if (right_l_vsplit->is_visible() || right_r_vsplit->is_visible()) {
		right_hsplit->show();
	} else {
		right_hsplit->hide();
	}
}
void EditorNode::_dock_select_input(const Ref<InputEvent> &p_input) {