For the second time in less than a year, Chicago-born R&B singer R. Kelly finds himself convicted of serious federal child-sex crimes and staring at a lengthy prison term. Last September, a jury in New York found him guilty of racketeering conspiracy charges alleging his musical career doubled as a criminal enterprise aimed at satisfying his predatory sexual desires — a case that resulted in a whopping 30-year sentence. The latest conviction came in U.S. District Court in Kelly’s hometown, where a jury on Wednesday found the “I Believe I Can Fly” singer guilty of sexually abusing his 14-year-o…