fetch-pack: don't needlessly copy fsck_options

fetch-pack: don't needlessly copy fsck_options

Change the behavior of the .gitmodules validation added in
5476e1efde (fetch-pack: print and use dangling .gitmodules,
2021-02-22) so we're using one "fsck_options".

I found that code confusing to read. One might think that not setting
up the error_func earlier means that we're relying on the "error_func"
not being set in some code in between the two hunks being modified
here.

But we're not, all we're doing in the rest of "cmd_index_pack()" is
further setup by calling fsck_set_msg_types(), and assigning to
do_fsck_object.

So there was no reason in 5476e1efde to make a shallow copy of the
fsck_options struct before setting error_func. Let's just do this
setup at the top of the function, along with the "walk" assignment.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>