fix(firebase_core, web): return empty list from apps getter in WASM mode

Fixes #17918

The `apps` getter now checks if the Firebase core module is loaded before
accessing `firebase.apps`. This avoids triggering a JavaScript exception
when Firebase is not initialized, which is more efficient than relying
on exception handling.

This change ensures `Firebase.apps` returns an empty list in both JS and
WASM web builds when called before `Firebase.initializeApp()`.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <[email protected]>

Author: davidmigloz

packages/firebase_core/firebase_core_web/lib/src/firebase_core_web.dart

@@ -227,6 +227,11 @@ class FirebaseCoreWeb extends FirebasePlatform {
   /// Returns all created [FirebaseAppPlatform] instances.
   @override
   List<FirebaseAppPlatform> get apps {
+    // Check if Firebase core module is loaded before accessing firebase.apps
+    if (globalContext.getProperty('firebase_core'.toJS) == null) {
+      return [];
+    }
+
     try {
       return firebase.apps.map(_createFromJsApp).toList(growable: false);
     } catch (exception, stackTrace) {

packages/firebase_core/firebase_core_web/test/firebase_core_web_exceptions_test.dart

@@ -39,4 +39,16 @@ void main() {
       });
     });
   });
+
+  group('apps getter', () {
+    setUp(() async {
+      FirebasePlatform.instance = FirebaseCoreWeb();
+    });
+
+    test(
+        'should return empty list when Firebase is not initialized',
+        () {
+      expect(FirebasePlatform.instance.apps, isEmpty);
+    });
+  });
 }