Fix request #4937: do not allow AgileDashboard with deleted trackers

Change-Id: I8ef403b4e20099cafd013231998c1807135bb780
Merge commit 'refs/changes/26/926/2' of ssh://gerrit.tuleap.net:29418/tuleap into stable

* ssh://gerrit.tuleap.net:29418/tuleap:
  Fix request #4937: do not allow AgileDashboard with deleted trackers

Conflicts:
	plugins/agiledashboard/include/autoload.php

Change-Id: Ib9a9048e9d3de8d5cd88890a38b7f0aba9ddb051
This is Tuleap 6.4.99.23

Change-Id: I1bb8137695f2d4a68795cf8b010e2037a1b810fd