Only call pa_cvolme set on stream creation if volume explicitly set.

Only call pa_cvolme set on stream creation if volume explicitly set.

Streams without a custom volume set use suitable volume selected
by the PulseAudio server. This is usually the correct choice, since then
stream-restore module can apply old volume to the stream. Also with
Sailfish explicitly setting the volume to streams breaks system volume.

Change-Id: I75f5bf4e7aaafb4bd55510f5ac4ddf03767d494b
Done-with: Juho Hämäläinen <juho.hamalainen@tieto.com>
Reviewed-by: Andrew den Exter <andrew.den.exter@qinetic.com.au>