Verify the default locale in case we're given an invalid one and need to fall back.

pkg/intl/example/basic/messages_all.dart

Index: pkg/intl/example/basic/messages_all.dart
diff --git a/pkg/intl/example/basic/messages_all.dart b/pkg/intl/example/basic/messages_all.dart
index 9265784b78d696baa7d1e632ad62d68336f54a07..75f6d028d51b355d94d82b5f52316215a6d4943c 100644
--- a/pkg/intl/example/basic/messages_all.dart
+++ b/pkg/intl/example/basic/messages_all.dart
@@ -32,7 +32,8 @@ initializeMessages(localeName) {
 }
 
 MessageLookupByLibrary _findGeneratedMessagesFor(locale) {
-  var actualLocale = Intl.verifiedLocale(locale, (x) => _findExact(x) != null);
+  var actualLocale = Intl.verifiedLocale(locale, (x) => _findExact(x) != null,
+      onFailure: (_) => null);
   if (actualLocale == null) return null;
   return _findExact(actualLocale);
 }