demux_edl: support global_tags with delay_open

The delay_open mechanism used by
--script-opt=ytdl_hook-all_formats=yes breaks setting metadata with
global_tags because tl->track_layout is NULL. See adcf51dccd cbb8f534b0
8ea7aa5471.

Fix this by applying tags to the EDL timeline in this case.

Tags must still be applied to tl->track_layout when available for them
to work with local EDL files.