console: add same surface replace pre-condition

Catch an invalid state early, before a potential use-after-free. This is
mainly useful for documentation purposes.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-id: 20170406120513.638-2-marcandre.lureau@redhat.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
