Fix PHP notice when editing artifact

Change-Id: I82748973ea8823b205a1f78dcd6496a78772294e
Merge commit 'refs/changes/77/1577/1' of http://gerrit.tuleap.net/tuleap into HEAD

* http://gerrit.tuleap.net/tuleap:
  Fix PHP notice when editing artifact

Change-Id: Ia71cbfaf3f62afbaafa794badf1653df4cefb511
This is Tuleap 6.8.99.3

Change-Id: Id5abf58160b6a9c99d4a18618d9dd7d41c716868