### 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
singleton->file_dialogs.insert(p_dialog);
}
void EditorNode::_file_dialog_unregister(FileDialog *p_dialog) {
	singleton->file_dialogs.erase(p_dialog);
}
void EditorNode::_editor_file_dialog_register(EditorFileDialog *p_dialog) {
	singleton->editor_file_dialogs.insert(p_dialog);
}
void EditorNode::_editor_file_dialog_unregister(EditorFileDialog *p_dialog) {
	singleton->editor_file_dialogs.erase(p_dialog);
}
Vector<EditorNodeInitCallback> EditorNode::_init_callbacks;
void EditorNode::_begin_first_scan() {
	OS::get_singleton()->benchmark_begin_measure("editor_scan_and_import");
	EditorFileSystem::get_singleton()->scan();
}
Error EditorNode::export_preset(const String &p_preset, const String &p_path, bool p_debug, bool p_pack_only) {
	export_defer.preset = p_preset;
	export_defer.path = p_path;
	export_defer.debug = p_debug;
	export_defer.pack_only = p_pack_only;
	cmdline_export_mode = true;
	return OK;
}
void EditorNode::show_accept(const String &p_text, const String &p_title) {