added wxTLW::ShouldPreventAppExit() which can be overridden to allow closing the application even if some windows are still opened; use it for wxHtmlHelpFrame

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@38607 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/html/helpfrm.h

@@ -106,6 +106,10 @@ public:
     virtual void AddToolbarButtons(wxToolBar* WXUNUSED(toolBar), int WXUNUSED(style)) {};
 
 protected:
+    // we don't want to prevent the app from closing just because a help window
+    // remains opened
+    virtual bool ShouldPreventAppExit() const { return false; }
+
     void Init(wxHtmlHelpData* data = NULL);
 
     void OnCloseWindow(wxCloseEvent& event);