double free in multipart processing

[whistlerwzc]

In function htp_ch_multipart_callback_request_body_data at htp_content_handlers.c,
if an error occurs while adding newly allocated params to tx->request_params, the func just returns without setting tx->request_mpartp->gave_up_data, thus there's a risk of double-free in htp_tx_destroy_incomplete.
However, i don't have any ideas on how to resolve it at present so i try to look up for some suggestions here,
Thx!

[victorjulien]

Closing in preparation of archiving the repo, see #467.