* Q1 GDP -0.3 pct s/adj q/q, worst since Q4 2008 (Reuters poll +0.3 pct): SEOUL (Reuters) - South Korea’s economy unexpectedly shrank in the first quarter, marking its worst performance since the global financial crisis, as government spending failed to keep up the previous quarter’s strong pace and as companies slashed investment. The shock contraction reinforced financial market views that the central bank is likely to make a U-turn on policy, shifting to an easing stance and possibly cutting interest rates to counter declining business confidence and growing external risks.