Improve error checking for dates.
Improve error checking for dates.

geographiclib/geographiclib,Sciumo/GeographicLib,geographiclib/geographiclib,geographiclib/geographiclib,geographiclib/geographiclib,Sciumo/GeographicLib,Sciumo/GeographicLib,Sciumo/GeographicLib,Sciumo/GeographicLib,Sciumo/GeographicLib,Sciumo/GeographicLib,Sciumo/GeographicLib