Fix RangeSlider throws an exception in a ListView (#135667)

fixes [[RangeSlider] [Flutter 3.10] LateInitializationError: Field '_startThumbCenter@280317193' has not been initialized.](flutter/flutter#126648)

### Code sample (Run it on iOS)

<details>
<summary>expand to view the code sample</summary> 

```dart
import 'package:flutter/material.dart';

void main() => runApp(const MyApp());

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @OverRide
  Widget build(BuildContext context) {
    return const MaterialApp(
      debugShowCheckedModeBanner: false,
      home: Example(),
    );
  }
}

class Example extends StatelessWidget {
  const Example({super.key});

  @OverRide
  Widget build(BuildContext context) {
    return Scaffold(
      body: ListView(
        children: <Widget>[
          const SizedBox(
            height: 1000,
            child: Placeholder(),
          ),
          RangeSlider(
            values: const RangeValues(0.25, 0.75),
            onChanged: (value) {},
          ),
        ],
      ),
    );
  }
}
```

</details>

Author: TahaTesser

packages/flutter/lib/src/material/range_slider.dart

@@ -900,8 +900,8 @@ class _RenderRangeSlider extends RenderBox with RelayoutWhenSystemFontsChangeMix
   late TapGestureRecognizer _tap;
   bool _active = false;
   late RangeValues _newValues;
-  late Offset _startThumbCenter;
-  late Offset _endThumbCenter;
+  Offset _startThumbCenter = Offset.zero;
+  Offset _endThumbCenter = Offset.zero;
   Rect? overlayStartRect;
   Rect? overlayEndRect;
 

packages/flutter/test/material/range_slider_test.dart

@@ -2541,7 +2541,7 @@ void main() {
     );
   });
 
-   testWidgetsWithLeakTracking('RangeSlider onChangeStart and onChangeEnd fire once', (WidgetTester tester) async {
+  testWidgetsWithLeakTracking('RangeSlider onChangeStart and onChangeEnd fire once', (WidgetTester tester) async {
     // Regression test for https://github.com/flutter/flutter/issues/128433
 
     int startFired = 0;
@@ -2581,4 +2581,34 @@ void main() {
     expect(startFired, equals(1));
     expect(endFired, equals(1));
   });
+
+  testWidgetsWithLeakTracking('RangeSlider in a ListView does not throw an exception', (WidgetTester tester) async {
+    // Regression test for https://github.com/flutter/flutter/issues/126648
+
+    await tester.pumpWidget(
+      MaterialApp(
+        home: Directionality(
+          textDirection: TextDirection.ltr,
+          child: Material(
+            child: ListView(
+              children: <Widget>[
+                const SizedBox(
+                  height: 600,
+                  child: Placeholder(),
+                ),
+                RangeSlider(
+                  values: const RangeValues(40, 80),
+                  max: 100,
+                  onChanged: (RangeValues newValue) { },
+                ),
+              ],
+            ),
+          ),
+        ),
+      ),
+    );
+
+    // No exception should be thrown.
+    expect(tester.takeException(), null);
+  });
 }