commit-graph: fix progress of reachable commits

To display a progress line while iterating over all refs, d335ce8f24 (commit-graph.c: show progress of finding reachable commits, 2020-05-13) should have added a pair of start_delayed_progress() and stop_progress() calls around a for_each_ref() invocation. Alas, the stop_progress() call ended up at the wrong place, after write_commit_graph(), which does all the commit-graph computation and writing, and has several progress lines of its own. Consequently, that new Collecting referenced commits: 123 progress line is overwritten by the first progress line shown by write_commit_graph(), and its final "done" line is shown last, after everything is finished: Expanding reachable commits in commit graph: 344786, done. Computing commit changed paths Bloom filters: 100% (344786/344786), done. Collecting referenced commits: 154, done. Move that stop_progress() call to the right place. While at it, drop the unnecessary 'if (data.progress)' condition protecting the stop_progress() call, because that function is prepared to handle a NULL progress struct. Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>