issue#263 return from hive_app_next_iteration when waiting for 'live' HAF

Previously, an application waited in app_next_iteration indefinitely for a moment when HAF reached the 'LIVE' stage what makes impossible to break with SIGINT and holds long-standing transaction. Now when HAF is before 'LIVE' then  app_next_iteration returns null block range after 500ms. Because no blocks range is returned application is forced to back ask again for blocks.