Bug 1339119 - Actually use the locale from macOS instead of throwing it away in OSPreferences::ReadSystemLocales. r=gandalf

intl/locale/mac/OSPreferences_mac.cpp

@@ -20,6 +20,7 @@ OSPreferences::ReadSystemLocales(nsTArray<nsCString>& aLocaleList)
 
   AutoTArray<UniChar, 32> buffer;
   int size = ::CFStringGetLength(userLocaleStr);
+  buffer.SetLength(size);
 
   CFRange range = ::CFRangeMake(0, size);
   ::CFStringGetCharacters(userLocaleStr, range, buffer.Elements());