Share Dialog does not require Login or any extended permissions

If is a Share dialog but FB app is not installed the WebDialog Builder fails. In Android all WebDialogs require a not null Session object.

Documentation for Android SDK FeedDialog:
https://developers.facebook.com/docs/reference/android/3.0/class/WebDialog.FeedDialogBuilder/

**session** The Session representing an authenticating user to use for showing the dialog; must not be null, and must be opened.