Fix for Iff768422c, use offset 0 when going back to work tree iterator

Fix for Iff768422c, use offset 0 when going back to work tree iterator

In Iff768422c the offset used for the content id was fixed to use  the
offset that applied to the dircache iterator. Unfortunately the index
for the dircache content id offset stuck for entries that were not in
the index. Few caller probably cared about that, unless it actually
caused an ArrayIndexOutOfBoundsException.

Change-Id: Ic9f0e77c8ea3a0770d88565e94392e76853e3006