AMERICAN Express Black Card holders, beware - this could happen to you. Music mogul Charlie Walk and magazine magnate Jason Binn rushed to Newark Airport the other day for a flight to Italy, where casino kingpin Steve Wynn was waiting for them on his yacht. But Walk didn't get past the metal detector. Sources say TSA offi cials took their sweet time searching him in a small, win dowless room where they lo cated his Black Card, made of titanium, in his shirt pocket. Walk and Binn barely made their flight. No wonder Wynn prefers cash.