修改 闪动的bug review by hongmo

@@ -85,9 +85,9 @@ export default class Header extends React.Component {
 
     handleNavigationChange(navState) {
         let heightT = parseInt(navState.title, 10) || 0; // turn NaN to 0
-        this.setState({
+        heightT>0?this.setState({
             realContentHeight: heightT,
-        });
+        }):null;
     }
 
     shouldStartLoadWithRequest(event) {