call OnInit() from all samples to allow using standard command line options with all of them (patch 1623971)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@44354 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

samples/notebook/notebook.cpp

@@ -34,6 +34,9 @@ IMPLEMENT_APP(MyApp)
 
 bool MyApp::OnInit()
 {
+    if ( !wxApp::OnInit() )
+        return false;
+
 #if wxUSE_HELP
     wxHelpProvider::Set( new wxSimpleHelpProvider );
 #endif