don't run the thread if its creation failed

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@31643 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

samples/thread/thread.cpp

@@ -726,6 +726,7 @@ void MyFrame::OnStartWorker(wxCommandEvent& WXUNUSED(event))
     if ( thread->Create() != wxTHREAD_NO_ERROR )
     {
         wxLogError(wxT("Can't create thread!"));
+        return;
     }
 
     m_dlgProgress = new wxProgressDialog