Changed preview renderer states to use construction and destruction instead of start and stop functions to make sure everything is shut down cleanly

Signed-off-by: Guthrie Adams <guthadam@amazon.com>

Gems/Atom/Tools/AtomToolsFramework/Code/Source/PreviewRenderer/PreviewRendererLoadState.cpp

@@ -13,31 +13,24 @@ namespace AtomToolsFramework
 {
     PreviewRendererLoadState::PreviewRendererLoadState(PreviewRenderer* renderer)
         : PreviewRendererState(renderer)
-    {
-    }
-
-    void PreviewRendererLoadState::Start()
     {
         m_renderer->LoadContent();
-        m_timeRemainingS = TimeOutS;
         AZ::TickBus::Handler::BusConnect();
     }
 
-    void PreviewRendererLoadState::Stop()
+    PreviewRendererLoadState::~PreviewRendererLoadState()
     {
         AZ::TickBus::Handler::BusDisconnect();
     }
 
     void PreviewRendererLoadState::OnTick(float deltaTime, [[maybe_unused]] AZ::ScriptTimePoint time)
     {
-        m_timeRemainingS -= deltaTime;
-        if (m_timeRemainingS > 0.0f)
-        {
-            m_renderer->UpdateLoadContent();
-        }
-        else
+        if ((m_timeRemainingS += deltaTime) > TimeOutS)
         {
             m_renderer->CancelLoadContent();
+            return;
         }
+
+        m_renderer->UpdateLoadContent();
     }
 } // namespace AtomToolsFramework