Fixes #5363 - Honor AllowedTypes on initial OpenDialog mixed-mode load

[Copilot]

Proposed Changes/Todos

• Ensure the initial mixed-mode file listing honors AllowedTypes even when Path is set before the dialog finishes initialization

  • FileDialog.EndInit () now refreshes any prebuilt state after assigning the initial CurrentFilter
  • This closes the gap where the first render showed all files until a directory change rebuilt state

• Add a focused regression test for the failing initialization order

  • Covers OpenMode.Mixed
  • Covers AllowedTypes configured before showing the dialog
  • Covers Path assigned before EndInit ()

• Behavior

  • Before: setting Path early could build State before CurrentFilter existed, so mixed mode showed unfiltered files until navigation refreshed the dialog
  • After: once the initial filter is established, any existing state is rebuilt immediately, so the first view is filtered correctly

using FileDialog fd = new OpenDialog ()
{
    OpenMode = OpenMode.Mixed,
    AllowedTypes = [new AllowedType ("View", ".Designer.cs")]
};

fd.Path = "/some/path";
fd.EndInit (); // now refreshes existing state after CurrentFilter is set

Pull Request checklist:

• I've named my PR in the form of "Fixes #issue. Terse description."
• My code follows the style guidelines of Terminal.Gui - if you use Visual Studio, hit CTRL-K-D to automatically reformat your files before committing.
• My code follows the Terminal.Gui library design guidelines
• I ran dotnet test before commit
• I have made corresponding changes to the API documentation (using /// style comments)
• My changes generate no new warnings
• I have checked my code and corrected any poor grammar or misspellings
• I conducted basic QA to assure all features are working

[Copilot]

Pull request overview

Updates FileDialog initialization so that when AllowedTypes is configured and Path is set before EndInit () completes, the initial mixed-mode listing is immediately rebuilt using the now-established CurrentFilter (avoiding an initially unfiltered first render).

Changes:

• In FileDialog.EndInit (), refreshes any pre-existing State after setting the initial CurrentFilter from AllowedTypes.
• Adds a regression test covering mixed-mode initialization where Path is assigned before EndInit (), ensuring AllowedTypes is respected on first load.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
Terminal.Gui/Views/FileDialogs/FileDialog.cs	Rebuilds existing state during EndInit () after establishing the initial type filter.
Tests/UnitTestsParallelizable/Views/FileDialogResultTests.cs	Adds regression test validating initial mixed-mode filtering when Path is set prior to EndInit ().

[tig]

Need @tznind to approve since he reported it.