Chicago’s federal court leads the nation in filings of digital file-sharing lawsuits. And that has cost a lot of pornography viewers money.Since 2009, 936 lawsuits have been filed in the U.S. District Court for the Northern District of Illinois alleging copyright infringement against individuals who downloaded movies — typically adult films — via an Internet protocol known as BitTorrent, a report from Lex Machina says.The next closest venue is the District of Colorado, where 601 file-sharing lawsuits were …