A stranger pushed a 35-year-old man onto Brooklyn train tracks in an unprovoked burst of violence over the weekend – marking the second random subway shove of the year , cops and sources said. The victim was standing on the southbound R train platform at 36th Street in Sunset Park around 4:55 a.m. Sunday, when the wacko walked up and knocked him onto the roadbed without saying a word, according to authorities and sources. The attacker bolted and had not been caught as of Monday afternoon,