Ensure previous focused instance exists before accessing it

Signed-off-by: Danilo Aimini <[email protected]>

Author: AMZN-daimini

Code/Framework/AzToolsFramework/AzToolsFramework/Prefab/PrefabFocusHandler.cpp

@@ -288,7 +288,10 @@ namespace AzToolsFramework::Prefab
         m_rootAliasFocusPathLength = aznumeric_cast<int>(AZStd::distance(m_rootAliasFocusPath.begin(), m_rootAliasFocusPath.end()));
 
         // Unset the DOM caching for previous focus and enabled it in new focus to optimize editing.
-        previousFocusedInstance->get().EnableDomCaching(false);
+        if (previousFocusedInstance.has_value())
+        {
+            previousFocusedInstance->get().EnableDomCaching(false);
+        }
         focusedInstance->get().EnableDomCaching(true);
 
         // Focus on the container entity in the Editor, if the interface is initialized.