Worker's Compensation; dispute over which workers' compensation insurance carrier is liable for payment to an employee of a subcontractor; application and interpretation of N.C.G.S. ?? 58-36-105 (required notice for cancellation of workers' compensation insurance), 58-36-110 (requirements for notifying policy holder of nonrenewal of insurance), and 97-19 (effect of general contractor?s not obtaining certificate of insurance from a subcontractor) when the subcontractor had workers' compensation insurance at the time of plaintiff's work-related accident