Fixed an exception when trying to display editor ui of an empty debug panel with overridden OnEditorGUI .

Assets/ScriptableRenderPipeline/Core/Debugging/DebugMenuUI.cs

         public void OnEditorGUI()
         {
             s_UIChanged = false;
-            m_DebugPanelUIs[m_ActivePanelIndex].OnEditorGUI();
+            if(!m_DebugPanelUIs[m_ActivePanelIndex].empty)
+                m_DebugPanelUIs[m_ActivePanelIndex].OnEditorGUI();
             if(s_UIChanged)
             {
                 UnityEditorInternal.InternalEditorUtility.RepaintAllViews();

Assets/ScriptableRenderPipeline/Core/Debugging/DebugPanelUI.cs

         protected List<DebugItemUI> m_ItemsUI = new List<DebugItemUI>();
         protected int               m_SelectedItem = -1;
 
+        public bool empty { get { return m_DebugPanel.itemCount == 0; } }
+
         public int itemCount { get { return m_ItemsUI.Count; } }
 
         public DebugPanelUI()