HPCC-11226 Add NULL check added to master in another commit

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>

ecl/hql/hqlfold.cpp

@@ -6069,7 +6069,8 @@ IHqlExpression * foldScopedHqlExpression(IHqlExpression * dataset, IHqlExpressio
 
     CExprFolderTransformer folder(NULL, foldOptions);
 
-    folder.setScope(dataset);
+    if (dataset)
+        folder.setScope(dataset);
 
     IHqlExpression * ret = folder.transformRoot(expr);