fix build when v8 is disabled (rfc 102)

Author: tbonfort

mapfile.c

@@ -5896,7 +5896,9 @@ int initMap(mapObj *map)
 
   msInitQuery(&(map->query));
 
+#ifdef USE_V8
   map->v8context = NULL;
+#endif
 
   return(0);
 }

mapobject.c

@@ -137,8 +137,10 @@ void msFreeMap(mapObj *map)
 
   msFreeQuery(&(map->query));
 
+#ifdef USE_V8
   if (map->v8context)
     msV8FreeContext(map);
+#endif
 
   msFree(map);
 }