If p4 reports a tag for a commit that git-p4 does not know
about (e.g. because it references a P4 changelist that was
imported prior to the point at which the repo was cloned into
git), make sure that the error is correctly caught and handled.
rather than just crashing.
Signed-off-by: Luke Diamand <luke@diamand.org> Signed-off-by: Junio C Hamano <gitster@pobox.com>