Fixed #503 background window flag

Fixed anotherr background window flag in case the background window is
defined last.

CHANGELOG.txt

@@ -11,6 +11,7 @@
 
 Changes:
 --------
+- 2017/09/11 (1.40.9) - Fixed window background flag if background window is declared last
 - 2017/08/27 (1.40.8) - Fixed `nk_item_is_any_active` for hidden windows
 - 2017/08/27 (1.40.7) - Fixed window background flag
 - 2017/07/07 (1.40.6) - Fixed missing clipping rect check for hovering/clicked

nuklear.h

@@ -18468,7 +18468,7 @@ nk_insert_window(struct nk_context *ctx, struct nk_window *win,
         ctx->active = ctx->end;
         ctx->end->flags &= ~(nk_flags)NK_WINDOW_ROM;
     } else {
-        ctx->end->flags |= NK_WINDOW_ROM;
+        /*ctx->end->flags |= NK_WINDOW_ROM;*/
         ctx->begin->prev = win;
         win->next = ctx->begin;
         win->prev = 0;