MinPlatformPkg/TestPointCheckLib: Add check for pointer Variable

Add check for pointer Variable to ensure it is not NULL when used.

Cc: Michael Kubacki <michael.a.kubacki@intel.com>
Cc: Chasel Chiu <chasel.chiu@intel.com>
Cc: Nate DeSimone <nathaniel.l.desimone@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Signed-off-by: Shenglei Zhang <shenglei.zhang@intel.com>
Reviewed-by: Chasel Chiu <chasel.chiu@intel.com>