LONDON (Reuters) – British actor Richard Griffiths, best known for his roles in 'Withnail and I' and the Harry Potter films, has died at the age of 65 after complications following heart surgery, his agent said on Friday. Griffiths spent almost four decades in radio, film, on television and on stage, and received some of his industry's top awards for his role in Alan Bennett's play "The History Boys". The portly actor filled the screen as the lascivious Uncle Monty in the cult 1987 film 'Withnail and I'. …