By Steve Hartman, Kerry BreenThere are few things sadder than a love story cut short by tragedy.    One such story comes out of a cemetery in Marshalltown, Iowa, where employees noticed that a goose, Blossom, was out of sorts after the death of her mate, Bud.  Steve Hartman has been a CBS News correspondent since 1998, having served as a part-time correspondent for the previous two years