Applied #10829: docview sample: enable canvas in --single mode

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@62087 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

samples/docview/docview.cpp

@@ -216,6 +216,7 @@ bool MyApp::OnInit()
     {
         m_canvas = new MyCanvas(NULL, frame);
         m_menuEdit = CreateDrawingEditMenu();
+        docManager->CreateNewDocument();
     }
 
     CreateMenuBarForFrame(frame, menuFile, m_menuEdit);