Make sure that a CupertinoDesktopTextSelectionToolbarButton doesn't c… (#173894)

This is my attempt to handle
https://github.com/flutter/flutter/issues/6537 for the
CupertinoDesktopTextSelectionToolbarButton UI control.

---------

Co-authored-by: Victor Sanni <victorsanniay@gmail.com>
Co-authored-by: Tong Mu <dkwingsmt@users.noreply.github.com>

packages/flutter/test/cupertino/desktop_text_selection_toolbar_button_test.dart

diff --git a/packages/flutter/test/cupertino/desktop_text_selection_toolbar_button_test.dart b/packages/flutter/test/cupertino/desktop_text_selection_toolbar_button_test.dart
index 9304464..f01e82b 100644
--- a/packages/flutter/test/cupertino/desktop_text_selection_toolbar_button_test.dart
+++ b/packages/flutter/test/cupertino/desktop_text_selection_toolbar_button_test.dart
@@ -127,4 +127,19 @@
     final CupertinoButton button = tester.widget(find.byType(CupertinoButton));
     expect(button.enabled, isFalse);
   });
+
+  testWidgets('CupertinoDesktopTextSelectionToolbarButton does not crash at zero area', (
+    WidgetTester tester,
+  ) async {
+    await tester.pumpWidget(
+      const CupertinoApp(
+        home: Center(
+          child: SizedBox.shrink(
+            child: CupertinoDesktopTextSelectionToolbarButton(onPressed: null, child: Text('X')),
+          ),
+        ),
+      ),
+    );
+    expect(tester.getSize(find.byType(CupertinoDesktopTextSelectionToolbarButton)), Size.zero);
+  });
 }