Add the missing check for NULL pointer before use it.

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@10116 6f19259b-4bc3-4df7-8a09-765794883524

MdeModulePkg/Universal/SetupBrowserDxe/IfrParse.c

@@ -1174,6 +1174,7 @@ ParseOpCodes (
       //
       if (CurrentExpression == NULL && MapScopeDepth > 0) {
         CurrentExpression = CreateExpression (CurrentForm);
+        ASSERT (MapExpressionList != NULL);
         InsertTailList (MapExpressionList, &CurrentExpression->Link);
         if (Scope == 0) {
           SingleOpCodeExpression = TRUE;
@@ -2120,6 +2121,7 @@ ParseOpCodes (
         //
         Status = PopCurrentExpression ((VOID **) &CurrentExpression);
         ASSERT_EFI_ERROR (Status);
+        ASSERT (MapScopeDepth > 0);
         MapScopeDepth --;
         break;