nkoverNk group NA

[Zabados]

I've just noticed that the function CorIndex and as a consequence all other functions returned nkoverNk with the group all as NA. The numbers are correct for the other column nkoverNk, so it isn't an issue that will change any results.

This is caused by dividing two data frames nk/Nk which of course it can't do for the land cover types if they are catagorical data (I think I had always ran the analysis with these as numbered land covers).

I'll fix this in the future.