progress: base progress estimates on queued extents, not completed ones

This means the progress table in the status output reflects the state of
the oldest task in the queue, not the newest.

Signed-off-by: Zygo Blaxell <bees@furryterror.org>

src/bees-roots.cc

@@ -1305,8 +1305,8 @@ BeesScanModeExtent::next_transid()
 		const auto this_crawl = found->second->crawl();
 		THROW_CHECK1(runtime_error, subvol, this_crawl);
 
-		// Get the last _completed_ state
-		const auto this_state = this_crawl->get_state_begin();
+		// Get the last _queued_ state
+		const auto this_state = this_crawl->get_state_end();
 
 		auto bytenr = this_state.m_objectid;
 		const auto bg_found = bg_info_map.lower_bound(bytenr);