ATHENS, Greece—Four Afghan asylum-seekers were sentenced to 10 years in prison in Greece on Saturday for their part in a fire that destroyed the Moria illegal immigrant camp last year, in a case that highlighted the chronic immigrant problem on Europe’s borders. The men, charged with arson with risk to human life over the fire on the island of Lesbos last September, were found guilty after a court rejected a request by lawyers for three of them to be tried by a juvenile court because they were under 18 at the time. Before the blaze, Moria was considered Europe’s biggest illegal immigrant camp, a sprawling and overcrowded town of tents and improvised shelters notorious for its poor and often dangerous living conditions. Described by rights groups and the U.N. refugee agency UNHCR as unfit for humans, the camp had become a symbol of Europe’s stumbling response to the immigration crisis …