HONGKONG astrologer Rebecca Nolan is hopping mad, and naturally who can she turn to but Keeping Posted for comfort. Her venom is aimed at a recent visitor to these shores, Jacqueline Stallone (son Sly is mentioned elsewhere in this column), who in a recent talk show appearance made the dubious claim that she was in the Guinness Book of World Records as the ''world's most accurate astrologer''. Hisses Rebecca: ''How then did she manage to miss three bad husbands, a robbery and a lawsuit? I'd say the Rambo of Pop Astrology should leave the real thing to the professionals.'' Pausing to take a deep breath and compose herself, the normally calm Rebecca added: ''Maybe, this sounds a bit strong, but people like Mother Rocky give astrology a black eye.'' Now, now, Rebecca. Let the fiery Jacky hear that and you risk one yourself.