NEW YORK — R. Kelly’s onetime manager was sentenced Monday to a year in federal prison for calling in a shooting threat that halted a screening of a damning documentary about the R&B star. The punishment won’t add to the time ex-manager Donnell Russell is already set to serve for a different effort to squelch sexual abuse claims against Kelly. Russell told a Manhattan federal judge Monday that he had “made bad judgments” while briefly working with the Grammy-winning, multiplatinum-selling singer.