don't crash if there's no wxFileSystem instance

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@26964 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/html/htmlpars.cpp

@@ -856,7 +856,8 @@ wxChar wxHtmlEntitiesParser::GetEntityChar(const wxString& entity)
 wxFSFile *wxHtmlParser::OpenURL(wxHtmlURLType WXUNUSED(type), 
                                 const wxString& url) const
 {
-    return GetFS()->OpenFile(url);
+    return m_FS ? m_FS->OpenFile(url) : NULL;
+    
 }