Melissa McCarthy’s genius is allowed out only for short walks in the disappointing new comedy “Identity Thief.” The rest of the time (an overlong 107 minutes), she’s chained to one of the more preposterous, logic-defying plots in recent memory, in which law enforcement in one state shrugs off felonies committed in another, abductees escape from captivity with the ease of Houdini, and the most important people in the life of Jason Bateman’s Sandy Bigelow Patterson treat him as if they’ve never met.