Initialize surface->link so we can always wl_list_remove() it

In particular, even if we never added it to the compositor surface list.
diff --git a/compositor/compositor.c b/compositor/compositor.c
index 2146c9b..29a1f52 100644
--- a/compositor/compositor.c
+++ b/compositor/compositor.c
@@ -129,6 +129,7 @@
 		return NULL;
 
 	wl_list_init(&surface->surface.destroy_listener_list);
+	wl_list_init(&surface->link);
 
 	glGenTextures(1, &surface->texture);
 	glBindTexture(GL_TEXTURE_2D, surface->texture);