Add NULL pointer check before using a pointer to avoid possible
NULL pointer dereference.
Cc: Eric Dong <eric.dong@intel.com>
Cc: Hao Wu <hao.a.wu@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Dandan Bi <dandan.bi@intel.com>
Reviewed-by: Hao Wu <hao.a.wu@intel.com>