get_sha1_1: allow octopus^12 to be properly parsed.

get_sha1_1: allow octopus^12 to be properly parsed.

We probably thought anybody who does more than 9 parents in an
Octopus is insane when this was initially done, but there is no
inherent reason to limit the number of independent topic
branches that happen to mature at the same time.

Our commit-tree allows up to 16 already, so at least we should
prepare to handle what we can produce, if only to be consistent.

Signed-off-by: Junio C Hamano <junkio@cox.net>