Hmmmm. To ding a performance by the Preservation Hall Jazz Band for being maybe just a bit too genteel wouldn’t make a lot of sense, would it? So we’ll just say that last night’s not-quite-two-hour concert by the venerated New Orleans jazz outfit’s current lineup at the Barns of Wolf Trap took a while to get cooking. But band and audience finally clicked after intermission, the players eventually convincing the initially staid crowd to…