mixer-control: Clear stream-ids from UI devices when BT stream loses all ports

mixer-control: Clear stream-ids from UI devices when BT stream loses all ports

Bluetooth streams can become portless so we can't just unconditionally add a
new UI device for devices without streams. Instead reset stream-ids from
existing streams that reference the stream that just became portless.

Signed-off-by: Guido Günther <agx@sigxcpu.org>
Origin: https://gitlab.gnome.org/GNOME/libgnome-volume-control/-/merge_requests/31
Bug: https://gitlab.gnome.org/GNOME/libgnome-volume-control/-/issues/34
Bug-Debian: https://bugs.debian.org/1126514
Applied-upstream: gnome-shell 50, commit:798230599950607ec285daecd070f5bcb28580e4

Gbp-Pq: Topic libgvc
Gbp-Pq: Name mixer-control-Clear-stream-ids-from-UI-devices-when-BT-st.patch