Welfare-fraud investigators were jolted into action yesterday after a front-page Herald report said they failed to follow up when a Dedham cop told them he found an EBT card and paperwork for other benefits during a raid on a Dorchester apartment loaded with drugs and cash.Dedham police Detective Bob Walsh said a representative from the state auditor’s Bureau of Special Investigations called him yesterday after the Herald reported his tip to the Department of Transitional Assistance went five weeks without an answer.