[3.x] Fix crash when casting from null

[timothyqiu]

The following script crashes Godot 3.4 beta5:

onready var node := get_node_or_null("the-node-does-not-exist") as Control

It does not crash in previous betas (or after removing the "as Control" part).

The crash MRP: TestAs.zip

---

_get_obj().rc was not checked for null, so it would crash due to null pointer dereference.

[RandomShaper]

Your fix makes sense. However, I've realized that I could have shortened this function when validity checks were made universal. Please, replace the full function by this one, which contains your null check in a different way (and test it a bit 😃):

ObjectID Variant::get_object_instance_id() const {
	if (unlikely(type != OBJECT)) {
		return 0;
	} else if (likely(_get_obj().rc)) {
		return _get_obj().rc->instance_id;
	} else if (likely(!_get_obj().ref.is_null())) {
		return _REF_OBJ_PTR(*this)->get_instance_id();
	} else {
		return 0;
	}
}

[akien-mga]

Thanks!