[Therion] Issue with magnetic declination calculation

I'm not sure if it is a bug or not, but I noticed that if I have one or more undated surveys I get a warning saying "Unable to compute magnetic declination for undated surveys." However if all of the surveys are undated I no longer get this warning and the output is uncorrected for declination. This is bad IMO because if you forgot to include the date in your survey files you would get an uncorrected output without realizing it. JP