use the focus client when the client is null for keyboard events

openbox/event.c

@@ -500,7 +500,8 @@ static void event_process(const XEvent *ec, gpointer data)
                        causes the window which appears to be focused to be
                        the one on which the actions will be executed */
                     keyboard_event((focus_cycle_target ?
-                                    focus_cycle_target : client), e);
+                                    focus_cycle_target :
+                                    (client ? client : focus_client)), e);
             }
         }
     }