call onHeightUpdated when height is valid

autoHeightWebView/index.ios.js

 
     handleNavigationStateChange(navState) {
         const height = Number(navState.title);
-        this.setState({ height });
-        if (this.props.onHeightUpdated) {
-            this.props.onHeightUpdated(height);
+        if (height) {
+            this.setState({ height });
+            if (this.props.onHeightUpdated) {
+                this.props.onHeightUpdated(height);
+            }
         }
     }
 

package.json

 {
   "name": "react-native-autoheightwebview",
-  "version": "0.0.5",
+  "version": "0.0.6",
   "description": "An auto height webview for React Native",
   "main": "autoHeightWebView",
   "scripts": {