bugfix: segfault might happen when using more_set_headers or more_clear_headers in the case that the nginx core initiated a 301 redirect. this issue was caused by an optimization in the nginx core where ngx_http_core_find_config_phase, for example, does not fully initialize the "Location" response header after creating the header. thanks Brian Akins for the original report in #7 and Vladimir Protasov for the insight in chaoslawful/lua-nginx-module#260.