By Greg Gilman LOS ANGELES (TheWrap.com) - Singer and actress Brandy Norwood gave a surprise performance in South Africa last Saturday during the Nelson Mandela Sports & Cultural day music concert, but there was one minor problem: Only 40 people were left in the 90,000-seat stadium to watch. The media just picked up on the unfortunate turnout Wednesday through Twitter chatter from the few who stayed to watch Norwood sing to - as South African musician Kabomo described - "an empty stadium. ...