ERR: preserve system error number in a few more places

It turns out that intialization may change the error number, so we
need to preserve the system error number in functions where
initialization is called for.
These are ERR_get_state() and err_shelve_state()

Fixes #7897

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7902)