Two misc bugfixes:

1) RayTracing will sometimes crash by dereferencing a null ptr.  This guards against it.
2) ViewportContext was missing some BusConnect / BusDisconnect calls.

Gems/Atom/Feature/Common/Code/Source/RayTracing/RayTracingFeatureProcessor.cpp

@@ -168,7 +168,7 @@ namespace AZ
                 return;
             }
 
-            if (m_rayTracingSceneSrg->IsQueuedForCompile())
+            if (!m_rayTracingSceneSrg || m_rayTracingSceneSrg->IsQueuedForCompile())
             {
                 //[GFX TODO][ATOM-14792] AtomSampleViewer: Reset scene and feature processors before switching to sample
                 return;

Gems/Atom/RPI/Code/Source/RPI.Public/ViewportContext.cpp

@@ -33,6 +33,7 @@ namespace AZ
                 nativeWindow,
                 &AzFramework::WindowRequestBus::Events::GetClientAreaSize);
             AzFramework::WindowNotificationBus::Handler::BusConnect(nativeWindow);
+            AzFramework::ViewportRequestBus::Handler::BusConnect(id);
 
             m_onProjectionMatrixChangedHandler = ViewportContext::MatrixChangedEvent::Handler([this](const AZ::Matrix4x4& matrix)
             {
@@ -48,6 +49,9 @@ namespace AZ
 
         ViewportContext::~ViewportContext()
         {
+            AzFramework::WindowNotificationBus::Handler::BusDisconnect();
+            AzFramework::ViewportRequestBus::Handler::BusDisconnect();
+
             if (m_currentPipeline)
             {
                 m_currentPipeline->RemoveFromRenderTick();