Add error message and return if we fail reading from a bucket in the

core_outout_filter(). core_output_filter() is in need of a rewrite, it is
getting quite crufty.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@89507 13f79535-47bb-0310-9956-ffa450edef68