Errors connected to extrapolating IGRF beyond last year of data ("unable to converge in ovt.util.EllipsoidtoEllipsoidic")

[Erik Johansson]

Extrapolating IGRF beyond the last year of data causes "unable to converge in ovt.util.EllipsoidtoEllipsoidic" (and GSM coordinates=NaN) for some years and likely some other errors as side effects.

(Solved before posting this. Only posted for documentation purposes.)

[Erik Johansson]

Internal caching of IGRF data combined with extrapolation beyond the last year of IGRF data caused errors and zero-value IGRF data which led to GSM coordinates=NaN and false IGRF data that was sometimes later used for faulty IGRF extrapolations (without error messages).

Bugfix permits extrapolation to any year after last IGRF data but with warning message for more than X years of extrapolation.