ATHENS (Reuters) - Greece's economy unexpectedly returned to growth in the second quarter despite deadlocked talks with foreign creditors and the threat of a Greek euro zone exit, data showed on Thursday. Gross domestic product expanded 0.8 percent from April to June, based on seasonally adjusted data from statistics service ELSTAT. A previously reported 0.2 percent decline in the first quarter was revised upward to 0 percent. The second quarter's flash estimate was above market expectations as analysts polled by Reuters were forecasting a 0.8 percent contraction quarter-on-quarter. ...