fix food tooltip for e.g. bountiful mutation

[llunak]

Without this, the food supply tooltip shows the calories rate of an original plant, but it should show double because of the double yield amount. See also Crop.InformationDescriptors().

test - mutants.sav.zip

Also, what is the status of #443 ? It's same like when I submitted it the first time. If you do not want it, just say so.