Checks for zoom_transition_runnable.

                    zoom_transition_runnable = new Runnable() {

                        public void run() {

                            // check just in case camera is closed or changed to a state where has_zoom==false,

                            // without cancelling the zoom_transition_runnable

                            if( camera_controller == null || !has_zoom ) {

                                return;

                            }

                            int this_zoom_value;

                            long time = System.currentTimeMillis() - start_time;

                            time += delay; // so we have a quicker transition