Backport: Link to unpublished document contains URL of non-published document

Just tested this on public GoGreen (7.8.3 community)

Reproduction:
Created two new news documents: "doc1" and "doc2"
Did not change anything in doc1
Created a link in doc2 to doc1
Saved doc2
Published doc2 (get a warning)

Expected:
Link goes to http://www.demo.onehippo.com/pagenotfound

Observed:
Link goes to http://www.demo.onehippo.com/news/2013/06/doc2.html