The heads of Magnolia Pictures nearly didn’t make it to their own premiere party the other night. During the Cinema Society bash for “Prince Avalanche” at the James Hotel, the freight elevator carrying the film company’s top brass and Halston model Pat Cleveland got stuck on the way up to the roof, we’re told, trapping 20 guests between floors for 15 minutes. A source says they emerged hot and shaken, with some joking that they needed to plunge into the Jimmy’s rooftop pool. Those who made it without incident to the Gents-sponsored bash included the film’s stars — Paul Rudd and Emile Hirsch — along with James Marsden and Ben Foster.