Workers’ compensation — Compensable accidents — Coronary artery disease — Presumption of compensability in case of law enforcement officer — Where claimant law enforcement officer satisfied all statutory prerequisites for entitlement to presumption that his coronary artery disease was work-related, including a disabling heart attack caused by coronary artery disease, it was error for judge of compensation claims to require claimant to establish a work-related cause of the purported “trigger” of his heart attack rather than keeping the burden on the employer/carrier to overcome the presumption of compensability of the coronary artery disease