There have been no shortage of schadenfreude-triggering box office flops this summer, but The Mortal Instruments: City of Bones weekend stumble to an approximately $9.3 million haul initially seems like a mystery. Weren’t Cassandra Clare’s Mortal Instruments books really popular? Doesn’t the story of an angst-ridden… » 8/25/13 6:00pm 8/25/13 6:00pm