David Carr reports on "The TV Set," screening Friday at the Tribeca Film Festival. "Where does bad television come from? "The TV Set," a movie that has its premiere tomorrow night at the Tribeca Film Festival, considers the question of agency, or blame, for the dreck that generally passes for the modern sitcom. As fate, or the process, would have it, everyone who touches the mythical pilot at the heart of the film manages to leave it a little worse for wear, most notably Lenny, the ferocious executive played by Sigourney Weaver."