### 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 (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();
	}
	for (int i = 0; i < DOCK_SLOT_MAX; i++) {
		if (dock_slot[i]->is_visible() && dock_slot[i]->get_tab_count()) {
			dock_slot[i]->set_current_tab(0);
		}
	}
	
	if (p_layout->has_section_key(p_section, "dock_filesystem_split")) {
		int fs_split_ofs = p_layout->get_value(p_section, "dock_filesystem_split");
		FileSystemDock::get_singleton()->set_split_offset(fs_split_ofs);
	}
	if (p_layout->has_section_key(p_section, "dock_filesystem_display_mode")) {
		FileSystemDock::DisplayMode dock_filesystem_display_mode = FileSystemDock::DisplayMode(int(p_layout->get_value(p_section, "dock_filesystem_display_mode")));
		FileSystemDock::get_singleton()->set_display_mode(dock_filesystem_display_mode);
	}
	if (p_layout->has_section_key(p_section, "dock_filesystem_file_sort")) {
		FileSystemDock::FileSortOption dock_filesystem_file_sort = FileSystemDock::FileSortOption(int(p_layout->get_value(p_section, "dock_filesystem_file_sort")));
		FileSystemDock::get_singleton()->set_file_sort(dock_filesystem_file_sort);
	}
	if (p_layout->has_section_key(p_section, "dock_filesystem_file_list_display_mode")) {