### 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_V_MSG(p_buffer_len < 11, ERR_INVALID_DATA, "Invalid sync packet received");
	bool is_delta = (p_buffer[0] & (1 << SceneMultiplayer::CMD_FLAG_0_SHIFT)) != 0;
	if (is_delta) {
		return on_delta_receive(p_from, p_buffer, p_buffer_len);
	}
	uint16_t time = decode_uint16(&p_buffer[1]);
	int ofs = 3;
	while (ofs + 8 < p_buffer_len) {
		uint32_t net_id = decode_uint32(&p_buffer[ofs]);
		ofs += 4;
		uint32_t size = decode_uint32(&p_buffer[ofs]);
		ofs += 4;
		ERR_FAIL_COND_V(size > uint32_t(p_buffer_len - ofs), ERR_INVALID_DATA);
		MultiplayerSynchronizer *sync = _find_synchronizer(p_from, net_id);
		if (!sync) {
			
			ofs += size;