Avoid to display empty DisplayNames for menu and title

When the Display name for a user is empty or emptied ( set to spaces or ...)
the title  of the page is weird and the menu display only the small arrow.

see the screenshot :

![oc_layout3](https://f.cloud.github.com/assets/177003/213018/c5de1764-834b-11e2-9ed2-cb7b4441e52e.jpg)

so i've choose to display the uid instead of the display name for the menu if it is empty