Fix empty symbol list

MarketDataLib/DataAccess/PortfolioDA.cs

@@ -149,6 +149,7 @@ namespace MarketData.DataAccess
 
         try
         {
+          if(null==symbols || 0==symbols.Count)return hasStopLimit;
           StringBuilder sb=new StringBuilder();
           if(null==symbols) return null;
           sqlConnection=SqlUtils.CreateMySqlConnection(MainDataSource.Instance.LocateDataSource("portfolio_data"));

MarketDataLib/DataAccess/PricingDA.cs

@@ -298,6 +298,7 @@ namespace MarketData.DataAccess
 
       try
       {
+        if(null == symbols || 0==symbols.Count)return latestDates;
         StringBuilder sb = new StringBuilder();
         sqlConnection = SqlUtils.CreateMySqlConnection(MainDataSource.Instance.LocateDataSource("market_data"));
         sb.Append(" select symbol, max(date) as date ");