libweston: assert make/model in weston_output_enable()

Output make and model are not allowed to be NULL in the protocol, so
ensure they are not forgotten when enabling an output.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Reviewed-by: Ian Ray <ian.ray@ge.com>
Reviewed-by: Daniel Stone <daniels@collabora.com>
Acked-by: Derek Foreman <derekf@osg.samsung.com>

libweston/compositor.c

@@ -5524,6 +5524,7 @@ weston_output_enable(struct weston_output *output)
 {
 	struct weston_compositor *c = output->compositor;
 	struct weston_output *iterator;
+	struct weston_head *head;
 	int x = 0, y = 0;
 
 	if (output->enabled) {
@@ -5538,6 +5539,11 @@ weston_output_enable(struct weston_output *output)
 		return -1;
 	}
 
+	wl_list_for_each(head, &output->head_list, output_link) {
+		assert(head->make);
+		assert(head->model);
+	}
+
 	iterator = container_of(c->output_list.prev,
 				struct weston_output, link);