Guard against null case and view when painting overlay and creating intersections

Four crashes reported from release builds share the same shape: a pointer that
is null during teardown or before a view is fully created is dereferenced
without a check.

RiuViewer::paintOverlayItems() used the owner case of the view and of the
comparison view without checking it, and dereferenced the result of a
dynamic_cast directly. The owner case is null while a case is being closed.

RicIntersectionFeatureImpl::createIntersectionBoxSlize() checked
activeMainOrComparisonGridView() but dereferenced activeGridView(), which is a
different object and can be null or have no viewer.

RimEclipseContourMapView::onCreateDisplayModel() called viewer()->mainCamera()
before the viewer exists.

RimCorrelationPlotCollection::applyFirstEnsembleFieldAddressesToPlot() called
front() on the ensemble parameter vector, which is empty for an ensemble
without realization parameters.

ApplicationLibCode/ProjectDataModel/ContourMap/RimEclipseContourMapView.cpp

@@ -210,7 +210,7 @@ void RimEclipseContourMapView::onCreateDisplayModel()
         updateGeometry();
     }
 
-    if ( viewer()->mainCamera()->viewMatrix() == sm_defaultViewMatrix )
+    if ( viewer() && viewer()->mainCamera() && viewer()->mainCamera()->viewMatrix() == sm_defaultViewMatrix )
     {
         zoomAll();
     }