Fix: Android crashs on call to _onWebViewEvent()
Fix: Android crashs on call to _onWebViewEvent()

I stress tested my app using:

```bash
adb shell monkey -p com.organization.app -c android.intent.category.LAUNCHER --kill-process-after-error -v 10000
```

It crashed quite often on the following line:

```js
oWebViewInterface._onWebViewEvent(eventName, jsonData);
```

telling me that a call to `_onWebViewEvent` on `undefined` was not possible.

This Pull Request fixes the crashing.
shripalsoni04/nativescript-webview-interface