libobs: Keep mixer data for placeholder sources

Placeholder sources are created when a plugin providing a source type is
unavailable. Since they're not marked as having audio any audio track
settings for them get lost. With this change we retain mixer information
if the source owns its id to avoid that.

libobs/obs-source.c

@@ -4905,7 +4905,8 @@ void obs_source_set_audio_mixers(obs_source_t *source, uint32_t mixers)
 
 	if (!obs_source_valid(source, "obs_source_set_audio_mixers"))
 		return;
-	if ((source->info.output_flags & OBS_SOURCE_AUDIO) == 0)
+	if (!source->owns_info_id &&
+	    (source->info.output_flags & OBS_SOURCE_AUDIO) == 0)
 		return;
 
 	if (source->audio_mixers == mixers)
@@ -4926,7 +4927,8 @@ uint32_t obs_source_get_audio_mixers(const obs_source_t *source)
 {
 	if (!obs_source_valid(source, "obs_source_get_audio_mixers"))
 		return 0;
-	if ((source->info.output_flags & OBS_SOURCE_AUDIO) == 0)
+	if (!source->owns_info_id &&
+	    (source->info.output_flags & OBS_SOURCE_AUDIO) == 0)
 		return 0;
 
 	return source->audio_mixers;