Guy Lodge Film CriticMort Rifkin, the ostensible novelist at the center of “Rifkin’s Festival,” has longterm writer’s block, and it’s hard to imagine that Woody Allen has ever empathized less with a character. Where Mort believes it’s futile to write if the finished work is not going to be on the level of Dostoevsky, the 84-year-old Allen continues churning out screenplays on an annual basis, unencumbered even by the increasingly distant memory of his own greatest work.