libedit: Prevent null dereference in popup

Lack of tool manager can happen when the popup is not connected to the
main tool.

Fixes: lp:1829825
* https://bugs.launchpad.net/kicad/+bug/1829825

common/tool/action_menu.cpp

@@ -321,7 +321,9 @@ void ACTION_MENU::OnMenuEvent( wxMenuEvent& aEvent )
 
     if( type == wxEVT_MENU_OPEN && m_Dirty )
     {
-        getToolManager()->RunAction( ACTIONS::updateMenu, true, this );
+        if( m_tool )
+            getToolManager()->RunAction( ACTIONS::updateMenu, true, this );
+
         aEvent.Skip();
         return;
     }