ignore broken messages of type 24
According to https://gpsd.gitlab.io/gpsd/AIVDM.html#_type_24_static_data_report, the part number field should be 0 or 1, while 2 and 3 are not allowed. We saw messages with value 3 in a data stream. Given the current API of the AIS module, the only sensible thing to do is to discard such data.
Edited by Steffen Michels