It’s difficult to even pick a starting point on the many misfires that are musician-turned-filmmaker Sia’s misguided directorial debut, “Music.” So much of it is bad and ill-conceived, all of it worth criticizing in various ways. There’s the infantilizing use of an autistic character, who the film portrays as nonverbal but never has the bravery to explicitly identify as autistic, who ends up being the magic push an adult screwup needs to get her life in order.