Declare wxBitmap in smaller scope in wxWizard DPI change handler

No real changes, just avoid creating wxBitmap unnecessarily and only do
it if we're really going to use it.

src/generic/wizard.cpp

@@ -904,9 +904,9 @@ void wxWizard::SetBitmap(const wxBitmapBundle& bitmap)
 
 void wxWizard::WXHandleDPIChanged(wxDPIChangedEvent& event)
 {
-    wxBitmap bmp;
     if ( m_statbmp )
     {
+        wxBitmap bmp;
         if ( m_page )
             bmp = m_page->GetBitmap();
         if ( !bmp.IsOk() )