Fix an issue in DIALOG_NETLIST: if the netlist filename does not exist, one cannot always modify the entered name.

(from master branch)

pcbnew/dialogs/dialog_netlist.cpp

@@ -294,6 +294,7 @@ void DIALOG_NETLIST::OnTestFootprintsClick( wxCommandEvent& event )
 void DIALOG_NETLIST::OnFilenameKillFocus( wxFocusEvent& event )
 {
     onFilenameChanged();
+    event.Skip();
 }