http: Make ap_die() robust against any HTTP error code and not modify
response status (finally logged) when nothing is to be done.


ap_die(): follow up to r1657881.

Use log level DEBUG for AP_FILTER_ERROR => HTTP_INTERNAL_SERVER_ERROR.
Submitted by: ylavic
Reviewed/backported by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1681114 13f79535-47bb-0310-9956-ffa450edef68