修复清算空头平仓交易时，交易结果方向错误的问题

Author: chenxy123

vn.trader/ctaAlgo/ctaBacktesting.py

@@ -517,7 +517,7 @@ def calculateBacktestingResult(self):
                         closedVolume = min(exitTrade.volume, entryTrade.volume)
                         result = TradingResult(entryTrade.price, entryTrade.dt, 
                                                exitTrade.price, exitTrade.dt,
-                                               -closedVolume, self.rate, self.slippage, self.size)
+                                               closedVolume, self.rate, self.slippage, self.size)
                         resultList.append(result)
 
                         # 计算未清算部分