output: added audio_output_closed()

The JACK output plugin needs to reset its "opened" flag when the JACK
server fails.  To prevent it from accessing the audio_output struct
directly introduce the API function audio_output_closed().

src/audioOutputs/audioOutput_jack.c

@@ -398,7 +398,7 @@ static int jack_playAudio(struct audio_output *audioOutput,
 	if ( jd->shutdown ) {
 		ERROR("Refusing to play, because there is no client thread.\n");
 		freeJackClient(jd);
-		audioOutput->open = 0;
+		audio_output_closed(audioOutput);
 		return 0;
 	}
 

src/output_api.c

@@ -22,3 +22,11 @@ const char *audio_output_get_name(const struct audio_output *ao)
 {
 	return ao->name;
 }
+
+void audio_output_closed(struct audio_output *ao)
+{
+	assert(ao->open);
+
+	ao->open = 0;
+}
+

src/output_api.h

@@ -101,4 +101,6 @@ extern struct notify audio_output_client_notify;
 
 const char *audio_output_get_name(const struct audio_output *ao);
 
+void audio_output_closed(struct audio_output *ao);
+
 #endif