### Godot version

4.1.dev4

### System information

Windows 10 - Godot 4.1.dev4 - Compatibility

### Issue description

When you syncronize 2 variables and both are in watched mode (taking out the "sync" property too) the server crashes

### Steps to reproduce

Create a MultiplayerSynchronizer, export 2 variables from a script, connect the server and the client and the server will crash instantly

In the project I give, the server and client are connected automatically when you use 2 debug instances when pressing play

### Minimal reproduction project

[minimalproject.zip](https://github.com/godotengine/godot/files/11665652/minimalproject.zip)

ERR_FAIL_COND(!spawn_queue.has(p_oid)); 
	
	if (p_oid != *(spawn_queue.begin())) {
		return;
	}
	for (const ObjectID &oid : spawn_queue) {
		ERR_CONTINUE(!tracked_nodes.has(oid));
		TrackedNode &tobj = tracked_nodes[oid];
		MultiplayerSpawner *spawner = get_id_as<MultiplayerSpawner>(tobj.spawner);
		ERR_CONTINUE(!spawner);
		spawned_nodes.insert(oid);
		if (multiplayer->has_multiplayer_peer() && spawner->is_multiplayer_authority()) {
			if (tobj.net_id == 0) {
				tobj.net_id = ++last_net_id;
			}
			_update_spawn_visibility(0, oid);
		}
	}
	spawn_queue.clear();
}
Error SceneReplicationInterface::on_despawn(Object *p_obj, Variant p_config) {