fix(neon): Fix list view flicker when loading

Signed-off-by: jld3103 <jld3103yt@gmail.com>

packages/neon/neon/lib/src/widgets/list_view.dart

@@ -54,16 +54,15 @@ class NeonListView extends StatelessWidget {
               itemCount: topFixedChildren!.length,
               itemBuilder: (final context, final index) => topFixedChildren![index],
             ),
-          if (isLoading)
+          SliverToBoxAdapter(
-            const SliverToBoxAdapter(
             child: NeonLinearProgressIndicator(
-                margin: EdgeInsets.symmetric(
+              visible: isLoading,
+              margin: const EdgeInsets.symmetric(
                 horizontal: 10,
                 vertical: 5,
               ),
             ),
           ),
-          if (error != null)
           SliverToBoxAdapter(
             child: NeonError(
               error,