shell: Make sure we actually have a resource in end_busy_cursor

It's actually possible to get here after the surface has been destroyed,
especially when running client apps under valgrind.

That probably shouldn't be able to segfault the compositor.

Signed-off-by: Derek Foreman <derekf@osg.samsung.com>
Reviewed-by: Bryce Harrington <bryce@osg.samsung.com>
1 file changed