Fix handling of buffered request body for per-location SSL

renegotiation when an internal redirect occurs:

* modules/ssl/ssl_engine_io.c (ssl_io_buffer_fill): Remove
protocol-level filters before inserting the buffering filter.
(ssl_io_filter_buffer): Return an EOS if invoked with an empty
brigade; do not remove the filter after exhausting the buffer.
(ssl_io_filter_buffer): Increase the type of the buffer filter to be
AP_FTYPE_PROTOCOL.

PR: 43738


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@591393 13f79535-47bb-0310-9956-ffa450edef68