Fixes race when a live stream finishes playing all segments from a
dynamic manifest and waits for its update. If the manifest meanwhile
changes from dynamic to static and this update is received
asynchronously, periodic calls of gst_adaptive_demux_manifest_update_cb
will stop. As a result the blocked stream won't get notified about the
updated manifest and will remain stuck indefinitely.
Also removed the wake-up code from gst_adaptive_demux_manifest_update_cb
where it remained as a relic from previous implementation when manifest
updates were synchronous.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/8587>
1248e4c462