GTK-require two-step in dataview

The before reset needs to be called in GTK prior to reseting the tree
otherwise, we will dereference items that may be cleared.

Fixes https://gitlab.com/kicad/code/kicad/issues/6672

pcbnew/dialogs/dialog_net_inspector.cpp

@@ -544,8 +544,9 @@ public:
 
     void deleteAllItems()
     {
+        BeforeReset();
         m_items.clear();
-        Cleared();
+        AfterReset();
     }