[PATCH weston] desktop-shell: NULL check whether a popup parent is a shell surface

[Olivier Fourdan]

> get_shell_surface(parent) may return NULL if the client passed a
> unassigned wl_surface or a wl_surface with a non-shell surface role
> (such as cursor role).
> 
> https://bugs.freedesktop.org/show_bug.cgi?id=92316
> 
> Signed-off-by: Jonas Ådahl <jadahl at gmail.com>

Tested-by: Olivier Fourdan <ofourdan at redhat.com>

Works for me :-)

Cheers,
Olivier