libobs: Fix audio issue with scene items

When a scene is added as a scene item with the same audio sources that
are already in the current scene, it would cause the current scene to no
longer output audio due to audio.

To replicate the issue, you would create two separate audio device
captures in scene 1, use add existing in scene 2 and add one of those
audio sources, then go back to scene 1, add scene 2 as a source, then
make scene 1 invisible.

libobs/obs-scene.c

@@ -907,7 +907,7 @@ static bool scene_audio_render(void *data, uint64_t *ts_out,
 
 	item = scene->first_item;
 	while (item) {
-		if (!obs_source_audio_pending(item->source)) {
+		if (!obs_source_audio_pending(item->source) && item->visible) {
 			uint64_t source_ts =
 				obs_source_get_audio_timestamp(item->source);