QNmeaPositionInfoSource doesn't provide any error reporting for invalid input data stream

Using a QNmeaPositionInfoSource plugged into a QSerialPort to process NMEA data stream from an external GPS receiver connected over a RS-232 UART connection. By eavesdropping on the QSerialPort readyRead() notification slot I can detect when there is no data coming from the receiver, however with the current lack of error reporting in the QNmeaPositionInfoSource class, I can't tell the difference between an invalid data stream (not NMEA sentences) and a receiver that is communicating appropriately but doesn't have a position fix.

In particular this can occur when there is a baud rate configuration mis-match between the GPS receiver and computer, as some RS-232 baud rate mismatches can result in the reception of a stream of valid (as far as the receiving UART is concerned) but nonsense characters rather than framing errors.