fetch-pack: free object filter before exiting

fetch-pack: free object filter before exiting

Our fetch_pack_args holds a filter_options struct that may be populated
with allocated strings by the by the "--filter" command-line option. We
must free it before exiting to avoid a leak when the program exits.

The usual fetch code paths that use transport.c don't have the same
leak, because we do the cleanup in disconnect_git().

Fixing this leak lets us mark t5500 as leak-free.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>