The wildest moment in the new Dave Chappelle special, “The Dreamer” (Netflix), arrives about two-thirds of the way through when the comic says he’s about to tell a long story. That’s not the unusual part. Some 36 years into a storied comedy career, Chappelle, 50, is better known for controversial yarns than carefully considered punchlines. At this point in the special, he tells the crowd in his hometown, Washington, D.C., that he is going to get a cigarette backstage, asks them to act as if he w