tasks #7148 - No picker is displayed for Themes with names which does not exist.

Change-Id: I8f3edfdf32adfcdfab930bb30e3c68a8d738a21a
Merge commit 'refs/changes/14/2714/3' of ssh://gerrit.tuleap.net:29418/tuleap into stable

* ssh://gerrit.tuleap.net:29418/tuleap:
  tasks #7148 - No picker is displayed for Themes with names which does not exist.
This is Tuleap 7.2.99.19

Change-Id: I6b226be4a4bf68059fd26decb2884d0dd5e5b397