Dave Chappelle was the unannounced opener for the Chris Rock-Kevin Hart double bill at Madison Square Garden on Saturday night. To Radiohead’s “Karma Police,” and wearing a white Nirvana In Utero shirt, the controversial comic came out smoking a cigarette without any introduction other than his white, green and red letter “C” logo on the LED screens. The capacity crowd greeted him with abundant applause and cheered whenever he brought up the topic of “cancel…