transport-helper: plug strbuf and string_list leaks

Transfer ownership of detached strbufs to string_lists of the
duplicating variety by calling string_list_append_nodup() instead of
string_list_append() to avoid duplicating and then leaking the buffer.

While at it make sure to release the string_list when done;
push_refs_with_export() already does that.

Reported-by: Jeff King <peff@peff.net>
Signed-off-by: Rene Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

transport-helper.c

@@ -881,7 +881,8 @@ static int push_refs_with_push(struct transport *transport,
 			struct strbuf cas = STRBUF_INIT;
 			strbuf_addf(&cas, "%s:%s",
 				    ref->name, oid_to_hex(&ref->old_oid_expect));
-			string_list_append(&cas_options, strbuf_detach(&cas, NULL));
+			string_list_append_nodup(&cas_options,
+						 strbuf_detach(&cas, NULL));
 		}
 	}
 	if (buf.len == 0) {
@@ -896,6 +897,7 @@ static int push_refs_with_push(struct transport *transport,
 	strbuf_addch(&buf, '\n');
 	sendline(data, &buf);
 	strbuf_release(&buf);
+	string_list_clear(&cas_options, 0);
 
 	return push_update_refs_status(data, remote_refs, flags);
 }
@@ -929,7 +931,8 @@ static int push_refs_with_export(struct transport *transport,
 		private = apply_refspecs(data->refspecs, data->refspec_nr, ref->name);
 		if (private && !get_oid(private, &oid)) {
 			strbuf_addf(&buf, "^%s", private);
-			string_list_append(&revlist_args, strbuf_detach(&buf, NULL));
+			string_list_append_nodup(&revlist_args,
+						 strbuf_detach(&buf, NULL));
 			oidcpy(&ref->old_oid, &oid);
 		}
 		free(private);