Fix unreleased feature - request #6276: be able to add a parent in the edit modal if no parent set

Change-Id: I725307befa9789fbcb439cb2c6e9b43a53bdf5e0
Merge commit 'refs/changes/97/1997/9' of ssh://gerrit.tuleap.net:29418/tuleap into stable

* ssh://gerrit.tuleap.net:29418/tuleap:
  Fix unreleased feature - request #6276: be able to add a parent in the edit modal if no parent set

Change-Id: I2b5c2ccd46f87aa2035b00e0a315ededb9aab95b
This is Tuleap 6.10.99.60

Change-Id: I4e5deff50f884e86e2cd1288f046f6b6f5e4a7bc