### Godot version

v4.0.beta17.mono.official [c40020513]

### System information

Window 11, Forward+, GTX 1060

### Issue description

Adding two theme variations in a row result to a  crash.

https://user-images.githubusercontent.com/93253123/217037249-1ce1d56d-beb6-4435-83ad-9f8a07fe0e96.mp4



### Steps to reproduce

1. Create a project.
2. Create a theme.
3. Double click to go in the theme editor.
4. Click on manage items buttons.
5. In the add type field type a name to add a type.
6. type another name to add a second type.
7. Crash.

### Minimal reproduction project

[ThemeVariationCrash.zip](https://github.com/godotengine/godot/files/10665863/ThemeVariationCrash.zip)

class SpinBox;
class TextureRect;
class EditorPropertyRevert {
public:
	static Variant get_property_revert_value(Object *p_object, const StringName &p_property, bool *r_is_valid);
	static bool can_property_revert(Object *p_object, const StringName &p_property, const Variant *p_custom_current_value = nullptr);
};
class EditorProperty : public Container {
	GDCLASS(EditorProperty, Container);
public:
	enum MenuItems {
		MENU_COPY_VALUE,
		MENU_PASTE_VALUE,
		MENU_COPY_PROPERTY_PATH,
		MENU_PIN_VALUE,
		MENU_OPEN_DOCUMENTATION,
	};
private:
	String label;
	int text_size;
	friend class EditorInspector;
	Object *object = nullptr;
	StringName property;
	String property_path;
	String doc_path;
	int property_usage;
	bool read_only = false;
	bool checkable = false;
	bool checked = false;
	bool draw_warning = false;