Fix mysql preconnect and release log

system/core.js

@@ -74,8 +74,8 @@ global.Core.Setting = {};
 if(Config && Config.Database.Mysql.on){
     let MysqlPool    = require(Core.Path.ExtraLib + '/mysql-pool.js').instance(Config.Database.Mysql);
     let testMysqlCon = MysqlPool.getConnection(function(err,connection){
-        connection.release();
         if(!err){
+            connection.release();
             connection.query('SELECT VERSION() as version',function(err,result,fields){
                 if(err){
                     LOGGER.error('Mysql Connect error,please recheck your config');
@@ -87,6 +87,9 @@ if(Config && Config.Database.Mysql.on){
                     global.MysqlDB   = require(Core.Path.Helper + '/mysqldb.js');
                 }
             });
+        }else{
+            LOGGER.error('Mysql Connect error,please recheck your config');
+            LOGGER.error(err);
         }
     });