Make sure that a TabPageSelector doesn't crash in 0x0 environment

[ahmedsameha1]

This is my attempt to handle #6537 for the TabPageSelector widget.

[gemini-code-assist]

Code Review

This pull request adds a regression test for an issue where TabPageSelector crashes when it has a zero size. The added test case is a good start, but it doesn't fully cover the scenario described in the issue, as it doesn't trigger a tab change. I've left a suggestion to improve the test to properly reproduce the crash condition. Additionally, the pull request seems to be missing the actual fix for the crash in TabPageSelector. Please ensure the fix is included before merging.

[gemini-code-assist]

This test case is intended to verify that TabPageSelector doesn't crash when it has a zero size, which is great. However, the current implementation only checks the initial build state. The crash described in the associated issue occurs when changing tabs while the widget has zero area, because the TabController's animation might not run correctly.

To properly test for the regression, the test should also trigger a tab change to ensure the crash condition is covered.

  testWidgets('TabPageSelector does not crash at zero area when changing tabs', (WidgetTester tester) async {
    final TabController controller = TabController(length: 2, vsync: tester);
    addTearDown(controller.dispose);

    await tester.pumpWidget(
      MaterialApp(
        home: Center(
          child: SizedBox.shrink(
            child: TabPageSelector(controller: controller),
          ),
        ),
      ),
    );
    expect(tester.getSize(find.byType(TabPageSelector)), Size.zero);

    // Change the tab index to trigger the animation that could cause a crash.
    controller.animateTo(1);
    await tester.pump(); // Start animation.
    // The test passes if it doesn't crash here.
    await tester.pumpAndSettle();
  });

[victorsanni]

Hi, can you resolve the merge conflicts?