lib-ssl-iostream: Shutdown connection cleanly whenever i/ostream is d…

…estroyed

Do this while both istream and ostream still exist. Fixes crash where
openssl_iostream_destroy() attempts to flush the shutdown, but ssl_input
is NULL and it crashes.

src/lib-ssl-iostream/istream-openssl.c

@@ -23,6 +23,7 @@ static void i_stream_ssl_destroy(struct iostream_private *stream)
 {
 	struct ssl_istream *sstream = (struct ssl_istream *)stream;
 
+	openssl_iostream_shutdown(sstream->ssl_io);
 	i_stream_free_buffer(&sstream->istream);
 	sstream->ssl_io->ssl_input = NULL;
 	ssl_iostream_unref(&sstream->ssl_io);

src/lib-ssl-iostream/ostream-openssl.c

@@ -26,6 +26,7 @@ static void o_stream_ssl_destroy(struct iostream_private *stream)
 	struct ssl_ostream *sstream = (struct ssl_ostream *)stream;
 	struct istream *ssl_input = sstream->ssl_io->ssl_input;
 
+	openssl_iostream_shutdown(sstream->ssl_io);
 	sstream->ssl_io->ssl_output = NULL;
 	i_stream_unref(&ssl_input);
 	ssl_iostream_unref(&sstream->ssl_io);