premiered Sunday at the Tribeca Film Festival exposes the frightening and vulnerable position actresses have been put in for decades on sets run by powerful male directors.Steamy sex scenes, they insist, are anything but sexy.Rosanna Arquette recalled that her first nude shoot, in the 1981 comedy “S.O.B.,” was never meant to happen. When she took the role, the actress said, the intimate moment was not mentioned in her contract.Then the cameras rolled.“Let’s just lose the bikini top,” Arquette, 62, remembers famed director Blake Edwards, whose wife Julie Andrews also went topless in the movie, telling her surrounded by crew and fellow actors, such as William Holden and Robert Preston.