Fixed SetZoom() so it can be used from the outside.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@2362 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/prntbase.cpp

@@ -752,10 +752,11 @@ void wxPrintPreviewBase::SetZoom(int percent)
         delete m_previewBitmap;
         m_previewBitmap = NULL;
     }
-    RenderPage(m_currentPage);
+
 
     if (m_previewCanvas)
     {
+        RenderPage(m_currentPage);
         m_previewCanvas->Clear();
         m_previewCanvas->Refresh();
     }