relay out the control after deleting any page, not just the last one (#9684); also extract the size event sending code in a separate function to be able to replace it with something better easier later

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@54613 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/listbook.h

@@ -112,6 +112,10 @@ private:
     // common part of all constructors
     void Init();
 
+    // this should be called when we need to be relaid out
+    void UpdateSize();
+
+
     DECLARE_EVENT_TABLE()
     DECLARE_DYNAMIC_CLASS_NO_COPY(wxListbook)
 };