change error handling for bad resp headers

 - avoid looping between ap_die and the http filter
 - remove the header that failed the check
 - keep calling apr_table_do until our fn stops matching


This is still not great. We get the original body, a 500 status
code and status line.

(r1773285 + fix for first return from check_headers)




Follow up to r1773293.
When check_headers() fails, clear anything (headers and body) from original/errorneous
response before returning 500.


Follow up to r1773761: don't check_headers() more than once.

Follow up to r1773761: don't recurse on internal redirects.

Follow up to r1773761: don't recurse on ap_send_error_response() either.

Follow up to r1773761: we need to check both ap_send_error_response() and internal redirect recursions.

Follow up to r1773761: improved recursion detection.
Submitted by: covener, ylavic, ylavic, ylavic, ylavic, ylavic, ylavic
Reviewed/backported by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1773995 13f79535-47bb-0310-9956-ffa450edef68