dbus_message_append_args_valist: Don't leak memory on inappropriate type

Found by source code inspection while trying to debug an unrelated
leak.

Signed-off-by: Simon McVittie <smcv@collabora.com>
Reviewed-by: Philip Withnall <withnall@endlessm.com>
Bug: https://bugs.freedesktop.org/show_bug.cgi?id=101568
(cherry picked from commit 6b7bdb105b)

dbus/dbus-message.c

@@ -1935,6 +1935,7 @@ dbus_message_append_args_valist (DBusMessage *message,
               _dbus_warn ("arrays of %s can't be appended with %s for now\n",
                           _dbus_type_to_string (element_type),
                           _DBUS_FUNCTION_NAME);
+              dbus_message_iter_abandon_container (&iter, &array);
               goto failed;
             }