Some devices don't have a card to match against, (e.g. network sinks),
which would make 'match_stream_with_devices()' get confused and log
warnings about missing card devices when trying to match streams with
devices.

Avoid this by marking a stream as 'in-possession' if there was already a
device with the stream ID set to it.

This fixes warning like

   (gnome-shell:3521215): Gvc-CRITICAL **: 10:57:07.155: gvc_mixer_card_get_index: assertion 'GVC_IS_MIXER_CARD (card)' failed