(svn r12918) -Fix [FS#1963] (r12679): last airport would always be shown as buildable even when it was not.

src/airport_gui.cpp

@@ -156,7 +156,7 @@ enum {
 	BAW_STR_INTERCONTINENTAL_AIRPORT,
 	BAW_HELISTATION,
 	BAW_LAST_AIRPORT = BAW_HELISTATION,
-	BAW_AIRPORT_COUNT = BAW_LAST_AIRPORT - BAW_SMALL_AIRPORT,
+	BAW_AIRPORT_COUNT = BAW_LAST_AIRPORT - BAW_SMALL_AIRPORT + 1,
 	BAW_BTN_DONTHILIGHT = BAW_LAST_AIRPORT + 1,
 	BAW_BTN_DOHILIGHT,
 };