server: don't send an error to NULL display_resource

if display_resource = wl_resource_create() fails in bind_display(),
we call wl_client_post_no_memory() which is wrong, since this function
uses display_resource (which is NULL at this point).
said simply: don't send an error to resource that you've just failed to create)

https://bugs.freedesktop.org/show_bug.cgi?id=91356



Reported-by: Ashim <ashim.shah@samsung.com>
Signed-off-by: Marek Chalupa <mchqwerty@gmail.com>
Reviewed-by: Derek Foreman <derekf@osg.samsung.com>
Reviewed-by: Bryce Harrington <bryce@osg.samsung.com>