Firefighters ruled Thursday a blaze that consumed an unoccupied Grass Valley cabin with a history of transient break-ins was caused by a person. Although who that person was and whether the fire was intentional remains to be determined, said Jeff Wagner, a Grass Valley Fire Department investigator. “We are still investigating, but we don’t know if it was accidental or not,” Wagner said. Shortly after 9:30 p.m. Wednesday, firefighters from Grass Valley, Nevada City, Ophir Hill and Nevada County Consolidated Fire Department responded to a reported structure fire on the 200 block of Fiddick Lane on the southeast side of …