fix sm2 encryption implementation bug.

fix sm2 encryption implementation bug.

According to the "GB/T 32918.4-2016"
section 6.1 encryption, step A5:
If result of the "KDF" is all zeros, we should go back to
the begin(step A1).

section 7.1 decryption, step B4:
If result of the "KDF" is all zeros, we should raise error and exit.

Signed-off-by: Liu-Ermeng <liuermeng2@huawei.com>
Reviewed-by: Neil Horman <nhorman@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/23210)