message: Checked if can navigate back in handler
diff: @@ -52,20 +52,21 @@ class NavigationMotion extends React.Component {
  return stateContext;
  }
  componentDidMount() {
  - if (this.props.crumb)
  BackHandler.addEventListener('hardwareBackPress', this.handleBack);
  }
  shouldComponentUpdate(props, state) {
  return state.navigationEvent === props.navigationEvent;
  }
  componentWillUnmount() {
  - if (this.props.crumb)
  BackHandler.removeEventListener('hardwareBackPress', this.handleBack);
  }
  handleBack() {
  - if (this.state.navigationEvent)
  + var {navigationEvent} = this.state;
  + if (navigationEvent && navigationEvent.stateNavigator.canNavigateBack(1)) {
  this.state.navigationEvent.stateNavigator.navigateBack(1);
  - return !!this.state.navigationEvent;
  + return true;
  + }
  + return false;
  }
  render() {
  var {navigationEvent} = this.state;
  