Add SecureBoot NULL pointer check before reference it. Contributed-under: TianoCore Contribution Agreement 1.0 Signed-off-by: Chao Zhang <chao.b.zhang@intel.com> Reviewed-by: Samer El-Haj-Mahmoud <elhaj@hpe.com> Reviewed-by: Qiu Shumin <shumin.qiu@intel.com>