Ensure SSL_has_pending() always works even before a connection

Ensure SSL_has_pending() always works even before a connection

s_client calls SSL_has_pending() even before the connection has been
established. We expect it to return 0 in this case and not put any errors
on the stack.

We change things so that SSL_has_pending() always returns 0 if there is
no stream available.

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Hugo Landau <hlandau@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/21578)