crash after copy paste of diagram (#434)

Hello,

I designed a use case diagram and do copy paste as PasteCopy of this diagram. Results is that I got an exception and the view of both diagrams fails (red cross displayed). I lost my work. Even the simp.back file fails to edit.

In the tree view I deleted the copied diagram but the original one still fails.

I can supply the simp file for analysis if necessary.

Here a copy the exception:

System.ArgumentOutOfRangeException: Index was out of range. Must be non-negative and less than the size of the collection.

Parameter name: index

at System.Collections.Generic.List`1.get_Item(Int32 index)

at SoftwareIdeasModeler.Core.DiagramItems.Special.DiagramDescription.DrawElement(DiagramDrawer drawer, DrawingParameters param)

at SoftwareIdeasModeler.Core.Projecting.ConcreteDiagramItem.Draw(DiagramDrawer drawer, DrawingParameters param)

at SoftwareIdeasModeler.Core.DiagramItems.ElementGroup.DrawElement(DiagramDrawer drawer, DrawingParameters param)

at SoftwareIdeasModeler.Core.Projecting.ConcreteDiagramItem.Draw(DiagramDrawer drawer, DrawingParameters param)

at SoftwareIdeasModeler.Visualisation.DiagramDrawer.Draw(DiagramLayer layer, ConcreteDiagramItem item)

at SoftwareIdeasModeler.Visualisation.DiagramDrawer.Draw(DiagramLayer layer, Rectangle clipArea)

at SoftwareIdeasModeler.Visualisation.DiagramDrawer.Draw(Diagram diagram, Rectangle drawBounds)

at SoftwareIdeasModeler.Core.Exporting.Images.BitmapDiagramExporter.GetThumbnail(Diagram diagram, Size size, Boolean optimized, Boolean fromZeroPosition)

at SoftwareIdeasModeler.Forms.EditorForm.GetThumbnail()

at SoftwareIdeasModeler.MainForm.UpdateWindowsTabSwitch()

at SoftwareIdeasModeler.MainForm.NotifyFormActivation(Form form)

at System.Windows.Forms.Form.OnEnter(EventArgs e)

at System.Windows.Forms.ContainerControl.UpdateFocusedControl()

Best Regards

Laurent