CSharp example custom interactor exception

[dmgroppe]

This CSharp example: https://lorensen.github.io/VTKExamples/site/CSharp/IO/ReadDICOMSeries/

Produces the following exception somewhat randomly:

System.Exception: 'error: could not get registered type - mteIndex='4294967295' classNameKey='''

If you scroll through enough slices, eventually you should get the exception. The exception appears to be caused by the custom vtkObjectEventHandlers that are added to interactorStyle on these two lines:

     interactorStyle.MouseWheelForwardEvt += new vtkObject.vtkObjectEventHandler(interactor_MouseWheelForwardEvt);
     interactorStyle.MouseWheelBackwardEvt += new vtkObject.vtkObjectEventHandler(interactor_MouseWheelBackwardEvt);