### 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)

AddedEditor ae;
	ae.property_editor = control;
	added_editors.push_back(ae);
}
void EditorInspectorPlugin::add_property_editor(const String &p_for_property, Control *p_prop, bool p_add_to_end) {
	AddedEditor ae;
	ae.properties.push_back(p_for_property);
	ae.property_editor = p_prop;
	ae.add_to_end = p_add_to_end;
	added_editors.push_back(ae);
}
void EditorInspectorPlugin::add_property_editor_for_multiple_properties(const String &p_label, const Vector<String> &p_properties, Control *p_prop) {
	AddedEditor ae;
	ae.properties = p_properties;
	ae.property_editor = p_prop;
	ae.label = p_label;
	added_editors.push_back(ae);
}
bool EditorInspectorPlugin::can_handle(Object *p_object) {
	bool success = false;
	GDVIRTUAL_CALL(_can_handle, p_object, success);
	return success;
}
void EditorInspectorPlugin::parse_begin(Object *p_object) {