Bug: Diet plan end date beyond current year plus one

If the start or end date of a diet plan in the diet calculator were outside the union of the range of years in the database and the current year plus one, the start and/or end year of the diet plan would not be included in the start and end date selection boxes, resulting in an incorrect date appearing in the form. This most often manifested itself when a long-term diet extends past the end of the year after the present. I added logic to make sure that the range of years included in the start and end date boxes includes the least of the current year and the first year of the diet plan minus one and the greatest of the next year and the last year of the diet plan plus one. (Reported by Jim Hollcraft.)