compositor: Initialize output listener links

Make sure the links are initialized so we can safely remove the listeners
in weston_view_unmap().

https://bugs.freedesktop.org/show_bug.cgi?id=72808
diff --git a/src/compositor.c b/src/compositor.c
index 5169921..6ca297a 100644
--- a/src/compositor.c
+++ b/src/compositor.c
@@ -451,8 +451,10 @@
 	view->output = NULL;
 
 	view->output_move_listener.notify = weston_view_output_move_handler;
+	wl_list_init(&view->output_move_listener.link);
 	view->output_destroy_listener.notify =
 		weston_view_output_destroy_handler;
+	wl_list_init(&view->output_destroy_listener.link);
 
 	return view;
 }