(Refiles to correct spelling of reporter’s name) By Pavel Polityuk and Vira Labych LVIV, Ukraine (Reuters) -Rescue workers were searching for survivors in the rubble of a theatre in the besieged city of Mariupol on Thursday, after Ukraine said a powerful Russian air strike hit the building where hundreds of people had been sheltering from the war. The port city is encircled by Russian forces and has seen fierce bombardment. A statement from the city council said that about 30,000 residents had managed to escape so far, but more than 350,000 remained stuck there. “The heart is breaking from wha…