Added type check to response in getStatus

When I use baseSModel.py and execute sendCommand to robotiq s model in short time, getStatus failes by following error.
I could avoid this error by this changes, but I think it is not good that getStatus has while loop in itself and I want to know why read_input_registers returns WriteMultipleRegistersResponse.
Is this problem caused by RobotiqHand firmware or pymodbus?

    File "/home/leus/ros/hydro/src/ros-industrial/robotiq_s_model_control/src/robotiq_s_model_control/baseSModel.py", line 155, in getStatus
        status = self.client.getStatus(16);
    File "/home/leus/ros/hydro/src/ros-industrial/robotiq_modbus_tcp/src/robotiq_modbus_tcp/comModbusTcp.py", line 89, in getStatus
        output.append((response.getRegister(i) & 0xFF00) >> 8)
    AttributeError: 'WriteMultipleRegistersResponse' object has no attribute 'getRegister'