Fix size glitch of WidgetsBookCtrl in widgets sample

The entire control is hidden until the dialog is resized.
This seems to be caused by (recent changes in) the wxPersistentManager.
This is fixed by populating the frame before restoring persistence.
(as is described in docs/doxygen/overviews/persistence.h.)

samples/widgets/widgets.cpp

@@ -381,8 +381,6 @@ bool WidgetsApp::OnInit()
 WidgetsFrame::WidgetsFrame(const wxString& title)
             : wxFrame(NULL, wxID_ANY, title)
 {
-    const bool sizeSet = wxPersistentRegisterAndRestore(this, "Main");
-
     // set the frame icon
     SetIcon(wxICON(sample));
 
@@ -514,6 +512,8 @@ WidgetsFrame::WidgetsFrame(const wxString& title)
 
     m_panel->SetSizer(sizerTop);
 
+    const bool sizeSet = wxPersistentRegisterAndRestore(this, "Main");
+
     const wxSize sizeMin = m_panel->GetBestSize();
     if ( !sizeSet )
         SetClientSize(sizeMin);