http: fix memory leak in fetch_and_setup_pack_index()

http: fix memory leak in fetch_and_setup_pack_index()

Inside the function `fetch_and_setup_pack_index()`, when the pack
obtained using `parse_pack_index()` fails to be verified by
`verify_pack_index()`, the function returns without closing and freeing
said pack.

Fix this by calling `close_pack_index()` to munmap the index file for
the leaking pack (which might have been mmapped by `fetch_pack_index()`
or `verify_pack_index()`), and then free it, when the verification
fails.

Signed-off-by: LorenzoPegorari <lorenzo.pegorari2002@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>