INDIAN RIVER COUNTY — An overnight fire at the Sweet Buffet restaurant, located just west of the Indian River Mall, has been determined to be arson, Fire Marshal Brian Nolan said Monday.Nolan would not release any other details about the blaze, except to say it began at 1:45 a.m. and investigators have determined the origin and cause of the fire. He did say the investigation was ongoing. Nolan said the roof was damaged by the blaze and there was smoke and water damage to kitchen and dining room. Sweet Buffet, located at 6700 20th Street, was formerly a Beef O’Brady’s restaurant.