Fixed a small leak in gradient computation
Fixed a small leak in gradient computation

yanqingmen/Wapiti,Jekub/Wapiti,yanqingmen/Wapiti,Neseb/wapiti,yanqingmen/Wapiti,yanqingmen/Wapiti,Neseb/wapiti,yanqingmen/Wapiti,Jekub/Wapiti