It almost happened to her last year at this time, and this year she's done it. Mary Higgins Clark rolls two number ones -- the top hardcover and mass market spots (and for the second week, no less) with Pretend You Don't See Her and Moonlight Becomes You. Simon &Schuster's official pub date for Pretend, the 15th novel by the doyenne of suspense fiction, is April 28; total copies in print after three printings is 900,000. Moonlight Becomes You, which spent 16 weeks on PW's hardcover list, was published by Pocket on April 9 with a first printing of 2.4 million. (For the record, it was Stephen King's serialized The Green Mile -- specifically, part one -- that kept Clark from landing both top spots last April