George Saunders’ short story “Escape from Spiderhead” is not, you might say, an obviously cinematic piece. So it’s an especially bold leap to use it as the inspiration for a starry, big budget, Netflix-subscriber-driving event movie, as they’ve done with “ Spiderhead,” which starts streaming Friday. It’s not surprising that the writers of “Deadpool” and “Zombieland” veered towards humor, but …
