zone-load: double free of configuration when journal apply / zonediff

fails

src/knot/server/zone-load.c

@@ -291,6 +291,8 @@ fail:
 			new_zone->contents = NULL;
 		}
 
+		/* Disconnect config, caller is responsible for it. */
+		new_zone->conf = NULL;
 		zone_free(&new_zone);
 	}