libobs: Call destroy signal after waiting

No real reason to have it above. Any other sources will still wait
anyway, so just makes things a bit more consistent.

libobs/obs-source.c

@@ -653,12 +653,12 @@ static void obs_source_destroy_defer(struct obs_source *source)
 {
 	size_t i;
 
-	obs_source_dosignal(source, "source_destroy", "destroy");
-
 	/* prevents the destruction of sources if destroy triggered inside of
 	 * a video tick call */
 	obs_context_wait(&source->context);
 
+	obs_source_dosignal(source, "source_destroy", "destroy");
+
 	if (source->context.data) {
 		source->info.destroy(source->context.data);
 		source->context.data = NULL;