reset: optionally setup worktree and refresh index on --mixed
Refreshing index requires work tree. So we have two options: always
set up work tree (and refuse to reset if failing to do so), or make
refreshing index optional.
As refreshing index is not the main task, it makes more sense to make
it optional. This allows us to still work in a bare repository to update
what is in the index.
Reported-by: Patrick Palka <patrick@parcs.ath.cx>
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>