Fix request #6805: diffs do not work on artifact modal comments

Change-Id: Ic13c0db9a99147a839a83d39759307811715963f
Merge commit 'refs/changes/77/2377/2' of ssh://gerrit.tuleap.net:29418/tuleap into tuleap-stable-master

* ssh://gerrit.tuleap.net:29418/tuleap:
  Fix request #6805: diffs do not work on artifact modal comments

Change-Id: Ib37fbcd1ae2498bfdffe60eed43047c516e9eb39
Tuleap 6.12.99.109

Change-Id: I89b47815775e8a3856efd112772080a4898cbf6c