- The bug would show up 
   - when using PS (so that we get re-execution)
   - the left_expr of the subquery is a reference to viewname.column_name, so that it crashes
      when one tries to use it without having called fix_fields for it.
   - when using SJ-Materialization, which makes use of sj_subq_pred->left_expr expression

- The fix is to have setup_conds() fix sj_subq_pred->left_expr for semi-join nests it finds.