QModbusDataUnit has inconsistent types for valueCount() and value()

getters\setters for length of the array use uint's.

getters\setters for accessing the values use int's.

This generates compiler and clang warnings about changing signedness - requiring lots of pointless casting to make the code clean.

void OnModbusReadComplete (const QModbusDataUnit *pData)
{
  for (int i=0; i<static_cast <int>(pData->valueCount ()); i++)
  {
    do_something_with_value (pData->value (i));
  }
}