Merge pull request #1112 from nanoric/fix_ctpGateway_onRspQryInvestorPosition_KeyError_before_qryInstrument

[Fix] ctpGateway: 修正一个在查询持仓时，若未查询过该合约大小则出错的BUG

vnpy/trader/gateway/ctpGateway/ctpGateway.py

@@ -734,6 +734,8 @@ class CtpTdApi(TdApi):
             pos.ydPosition = data['Position'] - data['TodayPosition']
             
         # 计算成本
+        if pos.symbol not in self.symbolSizeDict:
+            return
         size = self.symbolSizeDict[pos.symbol]
         cost = pos.price * pos.position * size