By Trevor Hunnicutt NEW YORK, May 16 (Reuters) - U.S. fund investors edged into stocks for the first time in four weeks, treating concern over the Iranian nuclear deal and Chinese-U.S. trade tensions as a buying opportunity, Investment Company Institute (ICI) data showed on Wednesday. Stock funds took in $2 billion during the week ended May 9, according to the trade group's data, which covers mutual funds and exchange-traded funds (ETFs) based in the United States. During that we