It's a diverting follow-up to "Meatballs," but it lacks the charm of the first one. Rudy Gerner, portrayed by Patrick Dempsey, finds himself working a summer job in upstate New York at a riverside place on the St. Lawrence River, where an eccentric woman (Sally Kellerman) offers guidance as he tries to win over girls. "Meatballs III: Summer Job" was filmed during the summer of 1984 but wasn't shown until early…