fix bug of NaN left style

src/NavigatorNavigationBar.js

@@ -140,6 +140,10 @@ class NavigatorNavigationBar extends React.Component {
       var component = this._components[componentName].get(this.props.navState.routeStack[index]);
       var props = this._getReusableProps(componentName, index);
       if (component && interpolate[componentName](props.style, amount)) {
+        if (isNaN(props.style.left)) {
+          props.style.left = undefiend;
+        }
+
         props.pointerEvents = props.style.opacity === 0 ? 'none' : 'box-none';
         component.setNativeProps(props);
       }