fill in flags parameter of HitTest() for all book controls; added new wxNB_HITTEST_ONPAGE bit

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@39719 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/bookctrl.cpp

@@ -186,9 +186,9 @@ void wxBookCtrlBase::OnHelp(wxHelpEvent& event)
             page = GetPage((size_t)pagePos);
         }
     }
-
-    if ( !page )
+    else // event.GetOrigin() != wxHelpEvent::Origin_HelpButton
     {
+        // if event came from keyboard then show the current page help
         page = GetCurrentPage();
     }