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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[TOPOLOGY]

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NetName=None

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Nodes=0x01

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Node64Present=0x01

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Node64Name=micromod

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Node64DCFName=PEAK MicroMod.eds

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EDSBaseName=eds