### 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
#include "editor_node.h"
#include "core/config/project_settings.h"
#include "core/input/input.h"
#include "core/io/config_file.h"
#include "core/io/file_access.h"
#include "core/io/resource_loader.h"
#include "core/io/resource_saver.h"
#include "core/object/class_db.h"
#include "core/object/message_queue.h"
#include "core/os/keyboard.h"
#include "core/os/os.h"
#include "core/os/time.h"
#include "core/string/print_string.h"
#include "core/string/translation.h"
#include "core/version.h"
#include "main/main.h"
#include "scene/gui/color_picker.h"