Carol Joynt, right, interviews D.C. Police Chief Cathy Lanier at a Q&A Cafe at Nathan’s. The Georgetown restaurant will close for good on July 12. It was just a month ago that Carol Joynt, the owner of Georgetown institution Nathan’s, sent out word that after months (years, really) of speculation, the restaurant had managed to secure a lease extension, and would, it seemed, therefore stay open. But in an email to patrons late today,…