heartrate: Fix D-Bus registration error case
heartrate: Fix D-Bus registration error case

If g_dbus_register_interface() fails, the struct heartrate_adapter
memory will be freed and therefore the heartrate_adapters list cannot
contain such an invalid pointer.

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