(svn r22538) -Fix [FS#4619]: possible crash when opening the airport build window for the first time

src/airport_gui.cpp

@@ -587,4 +587,5 @@ static void ShowBuildAirportPicker(Window *parent)
 void InitializeAirportGui()
 {
 	_selected_airport_class = APC_BEGIN;
+	_selected_airport_index = -1;
 }