A team of Mayer, Brown LLP lawyers won’t need to worry about paying for lunch for the immediate future. That’s because they received gift cards for sandwiches and cookies from Potbelly Corp. after representing the company in the initial public offering of its stock. Partners Edward S. Best and Jennifer J. Carlson and two associates represented Potbelly in the IPO that closed Wednesday. A running joke started among lawyers and bankers working on the deal about how everybody loved Potbelly’s food …