A teenager charged in the assault and robbery of 18-year-old actor Christopher Borgzinner on a Muni bus is scheduled to appear in San Francisco Superior Court today for a preliminary hearing. Uluao Mase, 18, is being charged with robbery, assault with force likely to cause great bodily injury and assault on a bus passenger in the Oct. 5 incident. Borgzinner, a San Francisco resident, is in the upcoming film “La Mission.”