wxUSE_LOG fixes.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@28338 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

samples/dialup/nettest.cpp

@@ -170,7 +170,9 @@ bool MyApp::OnInit()
     {
         wxLogError(wxT("The sample can't run on this system."));
 
+#if wxUSE_LOG
         wxLog::GetActiveTarget()->Flush();
+#endif // wxUSE_LOG
 
         // do it here, OnExit() won't be called
         delete m_dial;