Investors who allege Barnes & Thornburg LLP and one of its partners cost them $50 million in lost opportunities do not have a case for legal malpractice, a federal judge has held. In a written opinion, U.S. District Judge Joan H. Lefkow dismissed 11 malpractice claims against Barnes & Thornburg and 10 claims against Leslie J. Weiss. The investors based the claims on allegations that Weiss and the law firm deliberately breached the fiduciary duties they owe the funds managed by investment adviser The Nutmeg …