problems changing cursor in scribble-simple.c

[Cevat Ustun <ustun Glue umd edu>]

In an attempt to change the cursor in scribble-simple.c, 
I added the following declaration

GdkCursor *cursor;

and the following lines after the drawing_area declaration:

new_cursor=gdk_cursor_new(GDK_CROSS);
gdk_window_set_cursor(drawing_area->window, new_cursor);
gdk_cursor_destroy (new_cursor);

but I get the error

Gdk-CRITICAL **: file gdkwindow.c: line 1274
(gdk_window_set_cursor): assertion `window != NULL' failed.

and the cursor is not changed. Why? 

Cevat