Prevent segfaults after SSL renegotiation failures.

Prevent segfaults after SSL renegotiation failures.

* modules/ssl/ssl_engine_kernel.c (ssl_hook_Access): Set aborted flag
after renegotiation failure.

* modules/ssl/ssl_engine_io.c (ssl_filter_write, ssl_io_filter_output):
Don't dereference BIOs in filter_ctx when filter_ctx->pssl is NULL.
(ssl_filter_io_shutdown): Set aborted flag on abortive shutdown.

PR: 21370
Submitted by: Hartmut Keil <Hartmut.Keil@adnovum.ch>
Cleaned up by: Jeff Trawick, Joe Orton

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk/modules/ssl@100720 13f79535-47bb-0310-9956-ffa450edef68