Because Helen Harrison is an expert on 20th-century American art and has written about it, her latest book should not have come as a surprise. On the other hand, what would your reaction have been upon first encountering her first work of fiction, a paperback novel called “An Exquisite Corpse,” with a cover drawing of a figure wearing a dark mask with a chicken foot on one leg, a boot on one hand, and an umbrella in the other? Surprise!