Do not create a second default workboard column on existing disabled board
Summary:
A project workboard may have existed before but got disabled. When trying to access this workboard, do not trigger `buildInitializeContent()` which will create yet another default workboard column (and duplicates the existing column on the disabled workboard) but call `buildEnableContent()` which will display the "Workboard Disabled" panel instead allowing to re-enable the workboard.
Also fix some wrong indentation in a section below.
Closes T16475
Test Plan:
1. Create a new project.
2. Select "Workboard" from the left sidebar.
3. Select default "Columns: New Empty Board" for that project, and click the "Create Workboard" button.
4. In the right upper corner, select {nav icon=cog}, click {nav icon=cog,name=Manage Workboard}, and select {nav icon=ban,name=Disable Workboard}
5. End up on resulting http://phorge.localhost/project/board/1/, or go explicitly to that URI by selecting "Workboard" in the project navigation panel on the left
6. Before this patch, it shows the "Create Workboard" panel, allowing you to again select "Columns: New Empty Board", click the "Create Workboard" button, and see now two default columns both named "Backlog (Default)" on the (re-enabled) workboard
7. After this patch, it shows the "Disabled Workboard" panel with a button to re-enable the workboard
Reviewers: O1 Blessed Committers, mainframe98
Reviewed By: O1 Blessed Committers, mainframe98
Subscribers: tobiaswiese, valerio.bozzolan, Matthew, Cigaryno
Maniphest Tasks: T16475
Differential Revision: https://we.phorge.it/D26714