request #6909: Fix the list of submilestone trackers for a milestone.

Change-Id: I2f458514437c9c41146caa6c21953efa17768576
Merge commit 'refs/changes/24/3024/2' of ssh://gerrit.tuleap.net:29418/tuleap into tuleap-stable-master

* ssh://gerrit.tuleap.net:29418/tuleap:
  request #6909: Fix the list of submilestone trackers for a milestone.

Change-Id: Ic049d3548e7bba856827048b50b59fb16afb34dd
Tuleap 7.5.99.2

Change-Id: I4aaa3459d56bd7542bbcea68ef9e29452326b0ad