DataGrid UseDefaultDragAdorner with muliple selected rows

[std8590]

If I select one row in the datagrid and drag the row using "UseDefaultDragAdorner" I get this:

when I select multiple rows I don't get the DragAdorner.

Steps to reproduce the behavior:

1. Start the Showcase of the repository
2. Select DataGrid Tab
3. uncheck UseDefaultEffectDataTemplate
4. check UseDefaultDragAdorner
5. Select one row and drag
6. Select multiple rows and drag to see the differences

I would expect the same behavior with multiple rows.

If I fix the file DragDropPreview.cs line 238
from:
if (!this.UseDefaultDragAdorner && itemsCount <= maxItemsCount)
to
if (this.UseDefaultDragAdorner && itemsCount <= maxItemsCount)

it works!

[dcm99]

It would be nice if the DefaultAdorner could also be used for multiselection, but if one of the selected elements is no longer in the viewport, it may have been unloaded by the virtualization. It is therefore better to use a DragAdornerTemplate for multiselection.