Bug fix in rlmodbus.cpp

I have found a bug which makes Modbus functions 15 and 16 (WriteMultipleRegisters, WriteMultipleCoils) not work with serial line communications.

line 549 of rlmodbus.cpp:

    // mur was here: 2 x data[4] instead of data[4]/data[0]
          if(tty->readBlock(&data[4], byte_count+2, timeout) <= 0) return MODBUS_ERROR;
          memcpy(&tel[len],&data[4],byte_count+2); len += byte_count+2;

possibly the same applies in line 572:
         // mur was here: 2 x data[8] instead of data[8]/data[0]
          if(tty->readBlock(&data[8], byte_count+2, timeout) <= 0) return MODBUS_ERROR;
          memcpy(&tel[len],&data[8],byte_count+2); len += byte_count+2;

Kind regards,
Ernst