Fix crash on node view

In deallocated node state it is sometimes not possible
to view the node details anymore. Fixes
https://bugzilla.novell.com/show_bug.cgi?id=889834

(cherry picked from commit e1c3d040b53cb6069f837d2f80bb250352e05009)
Merge pull request #1139 from dirkmueller/release/stoney/master

Fix crash on node view