By Antony Currie The author is a Reuters Breakingviews columnist. The opinions expressed are his own. It was a bittersweet Thursday for Goldman Sachs. The Wall Street powerhouse received a double dose of good news from Washington, a rare and welcome event for investors and Chief Executive Lloyd Blankfein. First, the Securities and Exchange Commission dropped an investigation into a pre-crisis, Goldman-arranged $1.3 billion mortgage bond deal. Second, the U.S. Department of Justice decided it wouldn’t file criminal charges over the now-infamous Abacus deal. Yet Goldman was also forced to concede its legal worries are far from over.