libobs: Allow deferred source udpate on create

This allows sources to optionally defer update on creation in order to
prevent updates from being called from threads other than the video
thread.

libobs/obs-source.c

@@ -364,14 +364,14 @@ void obs_source_update(obs_source_t source, obs_data_t settings)
 {
 	if (!source) return;
 
-	obs_data_apply(source->context.settings, settings);
+	if (settings)
+		obs_data_apply(source->context.settings, settings);
 
-	if (source->context.data && source->info.update) {
-		if (source->info.output_flags & OBS_SOURCE_VIDEO)
-			source->defer_update = true;
-		else
-			source->info.update(source->context.data,
-					source->context.settings);
+	if (source->info.output_flags & OBS_SOURCE_VIDEO) {
+		source->defer_update = true;
+	} else if (source->context.data && source->info.update) {
+		source->info.update(source->context.data,
+				source->context.settings);
 	}
 }