Fixes #12971: A part of the login form disappears if the custom bar is not activated

[RaphaelGauthier]

https://www.rudder-project.org/redmine/issues/12971

[Normation-Quality-Assistant]

This PR breaks qa-test

-- stdout -- 
Your branch is behind 'NRM/branches/rudder/4.3' by 5 commits, and can be fast-forwarded.
  (use "git pull" to update your local branch)
Updating b10d891..12a04cd
Fast-forward
[...]
 * [new branch]      bug_12971/a_part_of_the_login_form_disappears_if_the_custom_bar_is_not_activated -> bug_12971/a_part_of_the_login_form_disappears_if_the_custom_bar_is_not_activated_pr
From github.com:Normation/rudder-plugins
   c79cf3b..a2522ff  branches/rudder/4.1 -> NRM/branches/rudder/4.1
   a22433d..054f2b1  branches/rudder/4.2 -> NRM/branches/rudder/4.2
   f19020d..12a04cd  branches/rudder/4.3 -> NRM/branches/rudder/4.3
   5e78885..0efb02d  master              -> NRM/master
Switched to branch 'branches/rudder/4.3'
Switched to a new branch '4.3_test'
No config file found, using default configuration

You should run ./qa-test in your repository to make sure it works.
You can also run rudder-dev merge https://github.com/Normation/rudder-plugins/pull/68 --test to test with upmerging.
After this, you can remove the qa: Can't merge ta
-- Your faithful QA

[fanf]

OK, merging this PR