AVRCP: Fix rejecting RegisterNotification if no transport exists
AVRCP: Fix rejecting RegisterNotification if no transport exists

If no transport exists set the volume as 0, the real volume will be set
when a transport becomes available.

silent-snowman/bluez,mapfau/bluez,pkarasev3/bluez,pstglia/external-bluetooth-bluez,pstglia/external-bluetooth-bluez,silent-snowman/bluez,pstglia/external-bluetooth-bluez,pkarasev3/bluez,ComputeCycles/bluez,silent-snowman/bluez,mapfau/bluez,mapfau/bluez,pstglia/external-bluetooth-bluez,ComputeCycles/bluez,mapfau/bluez,silent-snowman/bluez,pkarasev3/bluez,ComputeCycles/bluez,pkarasev3/bluez,ComputeCycles/bluez