Fix GetWorldPoint argument size in vtkResliceCursorRepresentation
A call to GetWorldPoint in vtkResliceCursorRepresentation was made with the argument worldFocalPoint of type double[3] instead of double[4].
This bug could causes stack corruption by writting worldFocalPoint[3].
This MR changes the type of worldFocalPoint variable used by GetWorldPoint from double[3] to double[4].