fsck is a repo-wide operation and should check all references no
matter which worktree they are associated to.
Reported-by: Jeff King <peff@peff.net> Helped-by: Elijah Newren <newren@gmail.com> Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>