Check for NULL pointer before dereference it.

Signed-off-by: Fu Siyuan <siyuan.fu@intel.com>
Reviewed-by: Ye Ting  <ting.ye@intel.com>
Reviewed-by: Dong Guo <guo.dong@intel.com>

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@14086 6f19259b-4bc3-4df7-8a09-765794883524

SecurityPkg/VariableAuthenticated/RuntimeDxe/Variable.c

@@ -808,6 +808,7 @@ Reclaim (
     //
     // Reinstall the new public key database.
     //
+    ASSERT (PubKeyHeader != NULL);
     CopyMem (CurrPtr, (UINT8*) PubKeyHeader, sizeof (VARIABLE_HEADER));
     Variable = (VARIABLE_HEADER*) CurrPtr;
     Variable->DataSize = NewPubKeySize;