do not allow negative padding
do not allow negative padding


Former-commit-id: 87fab5e72c5d13deb7ffea1f2df0bc26603156d9
Blahah/transrate,roryk/transrate,roryk/transrate,cboursnell/transrate,Blahah/transrate,cboursnell/transrate,roryk/transrate,cboursnell/transrate,Blahah/transrate