By Niket Nishant and Sukriti Gupta (Reuters) - The S&P 500 and the Nasdaq edged lower on Tuesday, the final day of the third quarter, on worries that a looming U.S. government shutdown could jeopardize the timely release of economic data. Sentiment turned risk averse a day after equities posted gains, underscoring how sensitive investors still are to any sign of uncertainty. While previous shutdowns have had a limited impact on markets, some analysts warned the current episode could be more disruptive g ...