dispatcher: spelling fix withing -> within

src/modules/dispatcher/doc/dispatcher.cfg

@@ -213,7 +213,7 @@ route[WITHINDLG] {
 		return;
 	}
 
-	# sequential request withing a dialog should
+	# sequential request within a dialog should
 	# take the path determined by record-routing
 	if (loose_route()) {
 		if (is_method("BYE")) {