And handle the case of a NULL buffer being returned cleanly, which is valid as long as a buffer list is returned instead. Previously this would cause an assertion because of calling gst_buffer_unref() with NULL. Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/6460>
Base classes ------------ GstBaseSink FIXME: not much point making it operate in pull mode as a generic base class I guess...