Fixed post_action to not trigger "header already sent" alert.
Fixed post_action to not trigger "header already sent" alert.

The alert was introduced in 03ff14058272 (1.5.4), and was triggered on each
post_action invocation.

There is no real need to call header filters in case of post_action,
so return NGX_OK from ngx_http_send_header() if r->post_action is set.

hy0kl/nginx,firebase/nginx,firebase/nginx,firebase/nginx,firebase/nginx,hy0kl/nginx,hy0kl/nginx