submodule--helper: free rest of "displaypath" in "struct update_data"

submodule--helper: free rest of "displaypath" in "struct update_data"

Fix a leak in code added in c51f8f94e5b (submodule--helper: run update
procedures from C, 2021-08-24), we clobber the "displaypath" member of
the passed-in "struct update_data" both so that die() messages in this
update_submodule() function itself can use it, and for the
run_update_procedure() called within this function.

Fix a leak in code added in 51f8f94e5b (submodule--helper: run update
procedures from C, 2021-08-24). We'd always clobber the old
"displaypath" member of the previously passed-in "struct update_data".

A better fix for this would be to remove the "displaypath" member from
the "struct update_data" entirely. Along with "oid", "suboid",
"just_cloned" and "sm_path" it's managing members that mainly need to
be passed between 1-3 stack frames of functions adjacent to this
code. But doing so would be a much larger change (I have it locally,
and fully untangling that in an incremental way is a 10 patch
journey).

So let's go for this much more isolated fix suggested by Glen. We
FREE_AND_NULL() the "update_data->displaypath", the "AND_NULL()" part
of that is needed due to the later "free(ud->displaypath)" in
"update_data_release()" introduced in the preceding commit

Moving ensure_core_worktree() out of update_submodule() may not be
strictly required, but in doing so we are left with the exact same
ordering as before, making this a smaller functional change.

Helped-by: Glen Choo <chooglen@google.com>
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Reviewed-by: Glen Choo <chooglen@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>