Imagine “The Tears of a Clown” as a film, with Adam Sandler instead of Smokey Robinson and Seth Rogen as his personal assistant, from the writer and director of The 40-Year-Old Virgin and Knocked Up. Judd Apatow’s third movie is distinctly his most ambitious. Which means it isn’t always funny. In a good way. Sandler plays a successful middle-aged comedy star whose jaded soul gets an existential jolt when he’s diagnosed with a potentially terminal disease and tries to reconnect with his now-married ex (Leslie Mann). That goes complicatedly. We have no shortage now of films whose subject is vulnerable male self-centeredness, but Apatow is approaching mastery of the form. It helps that he’s known his stars for a long time and fully understands their comic personas. More important is that he treats his characters so generously, articulating and allowing their flaws with grace and good humor. We get it: They’re not just funny; they’re people.