Continue traversal when rev-list --unpacked finds a packed commit.

Continue traversal when rev-list --unpacked finds a packed commit.

When getting the list of all unpacked objects by walking the commit history,
we would stop traversal whenever we hit a packed commit. However the fact
that we found a packed commit does not guarantee that all previous commits
are also packed. As a result the commit walkers did not show all reachable
unpacked objects.

Signed-off-by: Jan Harkes <jaharkes@cs.cmu.edu>
Signed-off-by: Junio C Hamano <junkio@cox.net>