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/listbox/lboxtest.cpp

@@ -322,6 +322,9 @@ END_EVENT_TABLE()
 
 bool LboxTestApp::OnInit()
 {
+    if ( !wxApp::OnInit() )
+        return false;
+
     wxFrame *frame = new LboxTestFrame(_T("wxListBox sample"));
     frame->Show();