Fix #10 by implementing fbd_dev_sound_stop
struct FbdDevSoundnew member
initable_initallocating the cancellable with
fbd_dev_sound_disposedisposing of the cancellable with
fbd_dev_sound_stopcancelling the cancellable with
g_cancellable_cancelbut also drop the cancellable and create a new one
The recreation of the cancellable is necessary b/c the
FdbDevSound object may be reused. If it is reused, the sound is immediately cancelled when started with the old cancellable.
There is the possibility to reset the cancellable but the documentation of g_cancellable_reset advises to remove the reference and create a new object.