A 49-year-old New Jersey man who thought he was meeting a 13-year-old girl on Tuesday to have sex was instead arrested by investigators. Richard J. Kostrub, of Somerdale, had ben communicating for about a month with someone he thought was a teenager on a chat app and via tex before agreeing to meet at the Walmart on Route 70 in Evesham, the Burlington County Prosecutor’s Office said. In reality, Kostrub had been in contact with an agent from the United States Department of Homeland Security, officials said. “Prior to orchestrating the rendezvous, Kostrub sent a nude photo of a young girl to th…