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

pkg/intl/lib/intl.dart

Index: pkg/intl/lib/intl.dart
diff --git a/pkg/intl/lib/intl.dart b/pkg/intl/lib/intl.dart
index 871fdc903aad7903873fa6c6d1d33001f8186c87..e6a3c7cec3738a756ccdc36e2b38d20e072b29fc 100644
--- a/pkg/intl/lib/intl.dart
+++ b/pkg/intl/lib/intl.dart
@@ -192,7 +192,10 @@ class Intl {
     // difficult. As a result, we call this more often. Consider keeping
     // verified locales for each purpose if it turns out to be a performance
     // issue.
-    if (newLocale == null) return getCurrentLocale();
+    if (newLocale == null) {
+      return verifiedLocale(getCurrentLocale(), localeExists,
+          onFailure: onFailure);
+    }
     if (localeExists(newLocale)) {
       return newLocale;
     }