Fix TypeError when tree expand/collapse/search is used before the tree finished loading

[Sebbeben]

Problem

The sidebar tree's collapseAll(), expandAll() and searchInput() Stimulus actions call methods on this._tree, which is only assigned in _fillTree() after the tree data has been fetched asynchronously (_getData() in reinitTree()).

If the expand-all / collapse-all button is clicked, or something is typed into the tree search box, before that fetch completes, this._tree is still null and the browser throws:

TypeError: Cannot read properties of null (reading 'expandAll')
    at ...tree_controller.js
    Error invoking action "click->elements--sidebar-tree#expandAll"

It is easy to hit on a cold cache / slow first load. The tree works normally once loaded — this is just an unhandled early interaction.

Fix

Guard the three actions with the controller's existing _isInitialized() helper (it already returns this._tree !== null), so they are no-ops until the tree is ready. One short guard per method; no behaviour change once the tree has loaded.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 60.04%. Comparing base (3b4fdf9) to head (3ec4089).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #1482      +/-   ##
============================================
- Coverage     60.06%   60.04%   -0.03%     
  Complexity     9057     9057              
============================================
  Files           675      675              
  Lines         29432    29432              
============================================
- Hits          17677    17671       -6     
- Misses        11755    11761       +6     

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[jbtronics]

looks good. Thanks.