Make sure that a CircleAvatar doesn't crash in 0x0 environment (flutter#173498)

This is my attempt to handle
flutter#6537 for the CircleAvatar UI
control.

Author: ahmedsameha1

packages/flutter/test/material/circle_avatar_test.dart

@@ -316,6 +316,14 @@ void main() {
       expect(paragraph.text.style!.color, equals(theme.primaryTextTheme.titleLarge!.color));
     });
   });
+
+  testWidgets('CircleAvatar renders at zero area', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      const MaterialApp(
+        home: SizedBox.shrink(child: CircleAvatar(child: Text('X'))),
+      ),
+    );
+  });
 }
 
 Widget wrap({required Widget child}) {