Let me say this more clearly.
Original sin is inferred from other parts of the Bible. The Bible is understood to be a consistent whole by my branch of Christianity. Therefore whatever is true for one book is true for all books. It does not have to be stated. Other parts of the Bible say clearly that there is NO one righteous, no not one. So applying these truths to the Book of Job we understand that Job's genuine righteousness is nevertheless imperfect or relative. Therefore it is possible for him to suffer. Yes, God decreed his suffering at the request of the devil. This is the reason for his suffering. But it would not have been possible if Job were perfectly righteous.