Older NAV files from BKG do not contain IONO CORR in header

[plutonheaven]

NAV files older than 2023-01-01 from the BKG http repo do not contain the iono correction in their header. We may want to find other repositories with such information, or be tolerant to missing header information.

Side note: the name for files older than 2023-01-01 change from BRDC00IGS_[...] to BRDC00WRD_[...].