Edited Issue: WPP crashes when deleting update [31]

There seems to be a problem with referenced updates.

```
************** Exception Text **************
System.InvalidOperationException: Das angegebene Update kann nicht gelöscht werden. ---> __System.Data.SqlClient.SqlException: The update cannot be deleted as it is still referenced by other update(s).
__ --- End of inner exception stack trace ---
at Microsoft.UpdateServices.Internal.BaseApi.SoapExceptionProcessor.DeserializeAndThrow(SoapException soapException)
at Microsoft.UpdateServices.Internal.DatabaseAccess.AdminDataAccessProxy.ExecuteSPDeleteUpdateByUpdateID(Guid updateID)
at Microsoft.UpdateServices.Internal.BaseApi.UpdateServer.DeleteUpdate(Guid updateId)
at Wsus_Package_Publisher.WsusWrapper.DeleteUpdate(IUpdate updateToDelete)
at Wsus_Package_Publisher.UpdateControl.updateDetailViewer1_DeleteUpdate(UpdateCollection updatesToDelete)
at Wsus_Package_Publisher.UpdateListViewer.mnuStripUpdateListViewer_ItemClicked(Object sender, ToolStripItemClickedEventArgs e)
at System.Windows.Forms.ToolStripDropDown.OnItemClicked(ToolStripItemClickedEventArgs e)
at System.Windows.Forms.ToolStrip.HandleItemClick(ToolStripItem dismissingItem)
at System.Windows.Forms.ToolStripItem.HandleClick(EventArgs e)
at System.Windows.Forms.ToolStripItem.HandleMouseUp(MouseEventArgs e)
at System.Windows.Forms.ToolStrip.OnMouseUp(MouseEventArgs mea)
at System.Windows.Forms.ToolStripDropDown.OnMouseUp(MouseEventArgs mea)
at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
at System.Windows.Forms.Control.WndProc(Message& m)
at System.Windows.Forms.ToolStrip.WndProc(Message& m)
at System.Windows.Forms.ToolStripDropDown.WndProc(Message& m)
at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)


************** Loaded Assemblies **************
mscorlib
Assembly Version: 4.0.0.0
Win32 Version: 4.0.30319.296 (RTMGDR.030319-2900)
CodeBase: file:///C:/Windows/Microsoft.NET/Framework64/v4.0.30319/mscorlib.dll
----------------------------------------
Wsus Package Publisher
Assembly Version: 1.1.1304.21
```

Trying to delete such a package causes WPP to crash.