### 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)

Node *node = Object::cast_to<Node>(p_obj);
	ERR_FAIL_COND_V(!node || p_config.get_type() != Variant::OBJECT, ERR_INVALID_PARAMETER);
	MultiplayerSynchronizer *sync = Object::cast_to<MultiplayerSynchronizer>(p_config.get_validated_object());
	ERR_FAIL_COND_V(!sync, ERR_INVALID_PARAMETER);
	sync->disconnect("visibility_changed", callable_mp(this, &SceneReplicationInterface::_visibility_changed));
	
	const ObjectID oid = node->get_instance_id();
	const ObjectID sid = sync->get_instance_id();
	ERR_FAIL_COND_V(!tracked_nodes.has(oid), ERR_INVALID_PARAMETER);
	TrackedNode &tobj = _track(oid);
	tobj.synchronizers.erase(sid);
	sync_nodes.erase(sid);
	for (KeyValue<int, PeerInfo> &E : peers_info) {
		E.value.sync_nodes.erase(sid);
		E.value.last_watch_usecs.erase(sid);
		if (sync->get_net_id()) {
			E.value.recv_sync_ids.erase(sync->get_net_id());
		}
	}
	return OK;
}
void SceneReplicationInterface::_visibility_changed(int p_peer, ObjectID p_sid) {