No longer crash if "Open in Addressbook" menu item is selected.
I found some BRs associated with this crash under the KMail product,
but there might be some under KNode too (I was too lazy too look).

The i18n string is re-used from other parts of KMail so it is not new.
Notice I'd like a better message once another string unfreeze happens.

Also note that a better solution is to disable this menu item if
we can precompute that the email address under the mouse is not
in the addressbook. Perhaps for KDE4.