free cleanup 12

Don't check for NULL before calling free function.  This gets:
        NAME_CONSTRAINTS_free GENERAL_SUBTREE_free ECDSA_METHOD_free
        JPAKE_CTX_free OCSP_REQ_CTX_free SCT_free SRP_VBASE_free
        SRP_gN_free SRP_user_pwd_free TXT_DB_free

Reviewed-by: Richard Levitte <levitte@openssl.org>