fetch-pack: fix memory leaks on fetch negotiation

We leak both the `nt_object_array` and `negotiator` structures in
`negotiate_using_fetch()`. Plug both of these leaks.

These leaks were exposed by t5516, but fixing them is not sufficient to
make the whole test suite leak free.

Signed-off-by: Patrick Steinhardt <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: pks-t

fetch-pack.c

@@ -2227,7 +2227,10 @@ void negotiate_using_fetch(const struct oid_array *negotiation_tips,
 	trace2_region_leave("fetch-pack", "negotiate_using_fetch", the_repository);
 	trace2_data_intmax("negotiate_using_fetch", the_repository,
 			   "total_rounds", negotiation_round);
+
 	clear_common_flag(acked_commits);
+	object_array_clear(&nt_object_array);
+	negotiator.release(&negotiator);
 	strbuf_release(&req_buf);
 }