### 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)

MAKE_ROOM( 1 +  4 + 8 + 4 + delta_mtu);
	uint8_t *ptr = packet_cache.ptrw();
	ptr[0] = SceneMultiplayer::NETWORK_COMMAND_SYNC | (1 << SceneMultiplayer::CMD_FLAG_0_SHIFT);
	int ofs = 1;
	for (const ObjectID &oid : p_synchronizers) {
		MultiplayerSynchronizer *sync = get_id_as<MultiplayerSynchronizer>(oid);
		ERR_CONTINUE(!sync || !sync->get_replication_config().is_valid() || !sync->is_multiplayer_authority());
		uint32_t net_id;
		if (!_verify_synchronizer(p_peer, sync, net_id)) {
			continue;
		}
		uint64_t last_usec = p_last_watch_usecs.has(oid) ? p_last_watch_usecs[oid] : 0;
		uint64_t indexes;
		List<Variant> delta = sync->get_delta_state(p_usec, last_usec, indexes);
		if (!delta.size()) {
			continue; 
		}
		Vector<const Variant *> varp;
		varp.resize(delta.size());
		const Variant **vptr = varp.ptrw();
		int i = 0;