If the VANC track does contain packets, but we skip over all packets, just treat it the same as if there hadn't been any packets at all and send a GAP event instead of erroring out with "Failed to handle essence element". We would error out because when we reach the end of the loop without having found a closed caption packet the flow return variable is still FLOW_ERROR which is what it has been initialised to. Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/1518>