### 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)

if (property == StringName()) {
		return Variant();
	}
	Dictionary dp;
	dp["type"] = "obj_property";
	dp["object"] = object;
	dp["property"] = property;
	dp["value"] = object->get(property);
	Label *drag_label = memnew(Label);
	drag_label->set_text(property);
	set_drag_preview(drag_label);
	return dp;
}
void EditorProperty::set_use_folding(bool p_use_folding) {
	use_folding = p_use_folding;
}
bool EditorProperty::is_using_folding() const {
	return use_folding;
}
void EditorProperty::expand_all_folding() {
}
void EditorProperty::collapse_all_folding() {
}
void EditorProperty::expand_revertable() {
}
void EditorProperty::set_selectable(bool p_selectable) {
	selectable = p_selectable;
}
bool EditorProperty::is_selectable() const {