libweston-desktop/xdg-shell-v6: Fix crash when surface has buffer at creation

libweston-desktop/xdg-shell-v6: Fix crash when surface has buffer at creation

When a surface has a buffer at creation time we send an error, which results
in a disconnection and all resources being destroyed.

Since we send that error and return before performing the configure_list init
weston_desktop_xdg_surface_destroy() will walk an uninitialized list and
dereference a NULL pointer.

Initializing the list earlier prevents this from happening.

Signed-off-by: Derek Foreman <derekf@osg.samsung.com>
Reviewed-by: Quentin Glidic <sardemff7+git@sardemff7.net>