fix: 2154 - refresh loading tile even without default error image

New file:
* `tile_error.dart`: Example of tile loading systematically failing.

Impacted files:
* `main.dart`: added the "Tile error" example
* `menu_drawer.dart`: added the "Tile error" example
* `tile_image.dart`: refresh the tile display even if there's no default error image

Author: monsieurtanuki

example/lib/main.dart

@@ -30,6 +30,7 @@ import 'package:flutter_map_example/pages/secondary_tap.dart';
 import 'package:flutter_map_example/pages/single_world_polys.dart';
 import 'package:flutter_map_example/pages/sliding_map.dart';
 import 'package:flutter_map_example/pages/tile_builder.dart';
+import 'package:flutter_map_example/pages/tile_error.dart';
 import 'package:flutter_map_example/pages/tile_loading_error_handle.dart';
 import 'package:flutter_map_example/pages/wms_tile_layer.dart';
 import 'package:flutter_web_plugins/url_strategy.dart';
@@ -55,6 +56,7 @@ class MyApp extends StatelessWidget {
         AbortObsoleteRequestsPage.route: (context) =>
             const AbortObsoleteRequestsPage(),
         PolylinePage.route: (context) => const PolylinePage(),
+        TileErrorPage.route: (context) => const TileErrorPage(),
         SingleWorldPolysPage.route: (context) => const SingleWorldPolysPage(),
         PolylinePerfStressPage.route: (context) =>
             const PolylinePerfStressPage(),

example/lib/pages/tile_error.dart

@@ -0,0 +1,41 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_map/flutter_map.dart';
+import 'package:flutter_map_example/widgets/drawer/menu_drawer.dart';
+
+/// Example of tile loading systematically failing.
+class TileErrorPage extends StatelessWidget {
+  static const String route = '/tile_error';
+
+  const TileErrorPage({super.key});
+
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      appBar: AppBar(title: const Text('Tile Error')),
+      drawer: const MenuDrawer(TileErrorPage.route),
+      body: FlutterMap(
+        options: const MapOptions(
+          initialZoom: 3,
+        ),
+        children: [
+          TileLayer(
+            // obviously wrong url template
+            urlTemplate: 'https://example.com/{z}/{y}/{x}',
+            tileBuilder: (context, tileWidget, tile) {
+              if (tile.loadError) {
+                return Center(
+                  child: Text('${tile.coordinates.z}'
+                      '/'
+                      '${tile.coordinates.x}'
+                      '/'
+                      '${tile.coordinates.y}'),
+                );
+              }
+              return tileWidget;
+            },
+          ),
+        ],
+      ),
+    );
+  }
+}

example/lib/widgets/drawer/menu_drawer.dart

@@ -34,6 +34,7 @@ import 'package:flutter_map_example/pages/secondary_tap.dart';
 import 'package:flutter_map_example/pages/single_world_polys.dart';
 import 'package:flutter_map_example/pages/sliding_map.dart';
 import 'package:flutter_map_example/pages/tile_builder.dart';
+import 'package:flutter_map_example/pages/tile_error.dart';
 import 'package:flutter_map_example/pages/tile_loading_error_handle.dart';
 import 'package:flutter_map_example/pages/wms_tile_layer.dart';
 import 'package:flutter_map_example/widgets/drawer/menu_item.dart';
@@ -162,6 +163,11 @@ class MenuDrawer extends StatelessWidget {
             routeName: ScaleBarPage.route,
             currentRoute: currentRoute,
           ),
+          MenuItemWidget(
+            caption: 'Tile error',
+            routeName: TileErrorPage.route,
+            currentRoute: currentRoute,
+          ),
           const Divider(),
           MenuItemWidget(
             caption: 'Repeated Worlds/Longitudes',

lib/src/layer/tile_layer/tile_image.dart

@@ -170,7 +170,7 @@ class TileImage extends ChangeNotifier {
     loadError = true;
 
     if (!_disposed) {
-      if (errorImage != null) _display();
+      _display();
       onLoadError(this, exception, stackTrace);
       onLoadComplete(coordinates);
     }
@@ -184,11 +184,6 @@ class TileImage extends ChangeNotifier {
     loadFinishedAt = DateTime.now();
 
     if (loadError) {
-      assert(
-        errorImage != null,
-        'A TileImage should not be displayed if loading errors and there is no '
-        'errorImage to show.',
-      );
       _readyToDisplay = true;
       if (!_disposed) notifyListeners();
       return;