SIGSEGV with to caml_unix_alloc_sockaddr

[talex5]

This program segfaults on OCaml 5.1.0:

let () =
  let a, b = Unix.(socketpair PF_UNIX SOCK_DGRAM 0) in
  let buf = Bytes.create 1 in
  while true do
    let sent = Unix.send_substring a "!" 0 1 [] in
    assert (sent = 1);
    let got, addr = Unix.recvfrom b buf 0 1 [] in
    assert (got = 1);
  done

$ ocamlopt -I +unix unix.cmxa test.ml && ./a.out
fish: Job 1, './a.out' terminated by signal SIGSEGV (Address boundary error)

(this was originally seen as an occasional hang in Eio's tests)

I believe this is due to this code in caml_unix_alloc_sockaddr failing to restore caml_state->local_roots on exit:

ocaml/otherlibs/unix/socketaddr.c

Lines 111 to 121 in c2476e3

	value caml_unix_alloc_sockaddr(union sock_addr_union * adr /*in*/,
	socklen_param_type adr_len, int close_on_error)
	{
	CAMLparam0();
	CAMLlocal1(a);
	value res;
	if (adr_len < offsetof(struct sockaddr, sa_data)) {
	// Only possible for an unnamed AF_UNIX socket, in
	// which case sa_family might be uninitialized.
	return alloc_unix_sockaddr(caml_alloc_string(0));
	}

[gasche]

This looks likely, would you like to submit a fix as a PR? (For example you could use CAMLreturn instead.)