Zmarties makes a number of fixes to the NMEA reader:

Zmarties makes a number of fixes to the NMEA reader:
* It makes invalid assumptions about the order of sentences,
specifically that it will receive a message with a date in it as the
first message
* it uses a uninitialized variable
* it treats invalid sentences as if they were valid
* it will accept a garbage truncated last line of the file as valid,
since the missing checksum on this line is not treated as an error