Fix incorrect bug log.

A missing tracing context in the SL_reply_out callback is perfectly valid - if you send from script a reply (se_send_reply) without doing any sip_trace() before.

modules/siptrace/siptrace.c

@@ -1663,7 +1663,7 @@ static void trace_slreply_out(struct sip_msg* req, str *buffer,int rpl_code,
 
 	info = context_get_ptr(CONTEXT_GLOBAL, current_processing_ctx, sl_ctx_idx);
 	if (info == NULL) {
-		LM_BUG("null trace info!something is wrong here \n");
+		LM_DBG("no sip_trace() done so far\n");
 		return;
 	}