When auto-compaction fails due to a locking error, we update the
statistics to indicate this failure. We're not doing the same when
performing a full compaction.
Fix this inconsistency by using `stack_compact_range_stats()`, which
handles the stat update for us.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>