Fixed crash when user attempts to activate SpanTreeCtrl root. It is now not possible to set that as the activated treeitem.
Fixed crash when user attempts to activate SpanTreeCtrl root. It
is now not possible to set that as the activated treeitem.

OverheadTransmissionLineSoftware/SpanAnalyzer,OverheadTransmissionLineSoftware/SpanAnalyzer,OverheadTransmissionLineSoftware/SpanAnalyzer,OverheadTransmissionLineSoftware/SpanAnalyzer