Glimpse: NullReferenceException on Get() for unpublished records.

Resolves #CMS-855

The ContentManager Get() is called twice for an item, once to get the item itself and once to determine whether or not the latest version is published or not. In the latter scenario, a call to get the item's content type throws a null reference exception because an item is unpublished (a second return value of null determins this).

This PR just adds a null check on the call to get an item's content type.

Low-risk, code-only change.