don't segfault on configfile error

git-svn-id: svn://svn.lighttpd.net/lighttpd/branches/lighttpd-merge-1.4.x@538 152afb58-edef-0310-8abb-c4023f1b3aa9

src/mod_trigger_b4_dl.c

@@ -90,6 +90,8 @@ FREE_FUNC(mod_trigger_b4_dl_free) {
 		size_t i;
 		for (i = 0; i < srv->config_context->used; i++) {
 			plugin_config *s = p->config_storage[i];
+
+			if (!s) continue;
 			
 			buffer_free(s->db_filename);
 			buffer_free(s->download_url);