ap_send_error_response: reset r->output filters to the protocol filters.

The equivalent logic was deleted when request filters were renamed to
RESOURCE filters.  This fixes the seg faults that sometimes happen on
daedalus after a bogus 416 HTTP response is generated.

In this case, includes_filter had found an <!--#include virtual > tag, and
sent a brigade representing the data before it down the filter chain.  The
byterange filter generated the bogus 416.  ap_send_error_response essentially
starts over with a new response, but it didn't do anything to clean up the
filter chain.  So the same instance of the includes_filter got driven from the
top with the canned error text and and EOS bucket, which confused the heck
out of it.  It inserted a sentinel from the original brigade into the
error page brigade, causing problems further down the filter chain.

Submitted by:	Greg Ames, Jeff Trawick


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@94662 13f79535-47bb-0310-9956-ffa450edef68