is_not_offered_this_year not accurate for multiple class entries

[dtemkin1]

For catalog entries with multiple classes, where some classes are offered in one semester and another isn't (eg. https://student.mit.edu/catalog/search.cgi?search=12.S492&style=verbatim), the function is_not_offered_this_year in catalog.py returns that neither are being offered in a semester. This causes both classes to not appear on Hydrant.

[rajendrakrshaw]

assign