Meg Zukin When Cazzie David dropped in on Chrissy Teigen to promote her new book, “No One Asked for This: Essays,” she found her friend worse for wear — until she realized the model and social media giant was not herself, but instead husband John Legend in a wig and silk robe.Legend played the role of his wife for Wednesday’s virtual Book Soup event without missing a beat, deftly answering David’s (and moderator Owen Thiele’s) questions in typical Teigen style (on the subject of Twitter, for