adummy: implement stop callback

modules/audio_output/adummy.c

@@ -88,6 +88,11 @@ static int Start(audio_output_t *aout, audio_sample_format_t *restrict fmt)
     return VLC_SUCCESS;
 }
 
+static void Stop(audio_output_t *aout)
+{
+    (void) aout;
+}
+
 static int Open(vlc_object_t *obj)
 {
     audio_output_t *aout = (audio_output_t *)obj;
@@ -97,7 +102,7 @@ static int Open(vlc_object_t *obj)
     aout->play = Play;
     aout->pause = Pause;
     aout->flush = Flush;
-    aout->stop = NULL;
+    aout->stop = Stop;
     aout->volume_set = NULL;
     aout->mute_set = NULL;
     return VLC_SUCCESS;