message: disallow custom window for export state
diff: @@ -250,6 +250,7 @@ ExportAggregateFunction::Bind(unique_ptr<BoundAggregateExpression> child_aggrega
  // this should be required
  D_ASSERT(bound_function.state_size);
  D_ASSERT(bound_function.finalize);
  + D_ASSERT(!bound_function.window);
  D_ASSERT(child_aggregate->function.return_type.id() != LogicalTypeId::INVALID);
  #ifdef DEBUG
  @@ -267,7 +268,7 @@ ExportAggregateFunction::Bind(unique_ptr<BoundAggregateExpression> child_aggrega
  bound_function.state_size, bound_function.initialize, bound_function.update,
  bound_function.combine, ExportAggregateFinalize, bound_function.simple_update,
  /* can't bind this again */ nullptr, /* no dynamic state yet */ nullptr,
  - /* can't propagate statistics */ nullptr, bound_function.window);
  + /* can't propagate statistics */ nullptr, nullptr);
  return make_unique<BoundAggregateExpression>(export_function, move(child_aggregate->children),
  move(child_aggregate->filter), move(export_bind_data),
  