Changed complex value slots to use NGX_CONF_UNSET_PTR. With this change, it is now possible to use ngx_conf_merge_ptr_value() to merge complex values. This change follows much earlier changes in ngx_conf_merge_ptr_value() and ngx_conf_set_str_array_slot() in 1452:cd586e963db0 (0.6.10) and 1701:40d004d95d88 (0.6.22), and the change in ngx_conf_set_keyval_slot() (7728:485dba3e2a01, 1.19.4). To preserve compatibility with existing 3rd party modules, both NULL and NGX_CONF_UNSET_PTR are accepted for now.