elementary_test: Fix warning about truncated string

gcc reports output between 7 and 17 bytes into a dest of size 16 so
increase destination size slightly

@fix

src/bin/elementary/test_ctxpopup.c

@@ -475,7 +475,7 @@ _list_item_cb11(void *data EINA_UNUSED, Evas_Object *obj, void *event_info EINA_
 {
    Evas_Object *ctxpopup;
    Evas_Coord x,y;
-   char label[16];
+   char label[18];
    int i = 0;
 
    if (list_mouse_down > 0) return;