By Alkis Konstantinidis and Horaci Garcia KRAMATORSK, Ukraine (Reuters) – When night falls in the Ukrainian city of Kramatorsk, just 20 km (12 miles) from the front line with Russia, police officers cruise through the dark and empty streets, looking for curfew violators, thieves and spies. The 65,000 people remaining in the eastern industrial city, which before the war had a population of around 150,000, have to stay inside from 10 p.m. until 4 a.m. Yet over the past week, police say they have found 33 violators: seven suspected spotters for Russian artillery, five looters – and 21 caught drin…