try to fix memory leak (#981)
try to fix memory leak (#981)

lijiarui/wechaty,Chatie/wechaty,wechaty/wechaty,wechaty/wechaty,mukaiu/wechaty,binsee/wechaty,binsee/wechaty,binsee/wechaty,mukaiu/wechaty,zixia/wechaty,Chatie/wechaty,lijiarui/wechaty,zixia/wechaty,Chatie/wechaty,mukaiu/wechaty,wechaty/wechaty