tg.sh: include non-tgish deps in preorder traversal
Since
872d9111 (tg.sh: support recurse_preorder traversal option,
topgit-0.14), recurse_deps has supported pre-order traversal in
addition to the normal post-order traversal.
However, non-tgish dependencies would have been omitted from any
pre-order traversal. Since only the summary --rdeps currently
makes use of pre-order traversal it's unlikely anything was
adversely affected as post-order traversal did included those deps.
Correct the logic error and include non-tgish deps in the pre-order
traversal output like they should have been from the beginning.
Signed-off-by: Kyle J. McKay <mackyle@gmail.com>