streamline nmea_ndeg2degree and nmea_degree2ndeg
streamline nmea_ndeg2degree and nmea_degree2ndeg

work around a curious failure in which a call to
nmea_ndeg2degree results in a NaN value while that
should not happen

Signed-off-by: Ferry Huberts <66e11f9f5d965b69497c7e73d5e808f8b13c1218@pelagic.nl>

AHR-Project/nmealib,AHR-Project/nmealib