self->eos was never reset after streamsynchronizer has sent EOS
(except on explicit flush or switching back to PAUSED).
As a result, synchronization was broken if new streams were pushed later
as gst_stream_synchronizer_wait() does not wait if self->eos is set.
Fix this by reseting self->eos on STREAM_START as that means a new
stream is being sent upstream and so a new EOS will follow later on.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/4755>
GST_STREAM_SYNCHRONIZER_LOCK (self);
self->have_group_id &= have_group_id;
have_group_id = self->have_group_id;
+ self->eos = FALSE;
stream = gst_streamsync_pad_get_stream (pad);