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

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                  <xsd:element name="Linux">

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                    <xsd:complexType>

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                      %(toolchain_gcc)s

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                    </xsd:complexType>

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                  </xsd:element>