commit-reach: die on contains walk errors

commit-reach: die on contains walk errors

Without generation numbers, repo_is_descendant_of() can return -1 when
it cannot read commit ancestry. commit_contains() exposes that result
through a Boolean interface, so ref-filter treats it as true. This can
include a ref for --contains or exclude it for --no-contains without
failing the command.

Die when repo_is_descendant_of() reports an error. The memoized walk
already dies when it cannot parse a commit, so callers of the
non-memoized path no longer turn a failed walk into a match.

Reported-by: Jeff King <peff@peff.net>
Signed-off-by: Tamir Duberstein <tamird@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>