fix twice shown error message box, when wrong non-valid IEC identifier entered

It happens when non-valid name for variable name or name of field in
structure entered. This issue is described in details here:
http://trac.wxwidgets.org/ticket/16333

<?xml version="1.0" encoding="UTF-8"?>
<BeremizRoot URI_location="LOCAL://">
  <TargetType/>
</BeremizRoot>