Fix GetLength.

The distance in the representation is only recomputed when the
 representation is updated. This means that if the bone's representation
exist but isn't displayed (and thus recomputed), the distance will never
be updated. That's why we simply recompute it all the time.

Issue #13621

Libs/VTK/Widgets/vtkBoneWidget.cxx

@@ -863,11 +863,6 @@ void vtkBoneWidget::SetLocalTailRest(double tail[3])
 //----------------------------------------------------------------------------
 double vtkBoneWidget::GetLength()
 {
-  if (this->GetBoneRepresentation())
-    {
-    return this->GetBoneRepresentation()->GetLength();
-    }
-
   double lineVect[3];
   vtkMath::Subtract(this->GetCurrentWorldTail(),
     this->GetCurrentWorldHead(), lineVect);