You cannot get name of IsolatedStorageFileStream the normal way

It always returns `"[unknown]"` (making it pass the checks against `null`), but it will not contain the actual value.

This change will check for the special case (i.e. if `fileStream` is an instance of `System.IO.IsolatedStorage.IsolatedStorageFileStream`) and then get the filename by casting the `filestream` to it's original `System.IO.IsolatedStorage.IsolatedStorageFileStream`.