Fixing aliasing issue when index doesn't exist

What
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The problem is if you use Tire.index('foobaz').aliases it causes an error instead of returning a blank array.

This aims to fix that by returning [] for anything that's not a 200 status code.


How to test
========

The spec should show you how to test the code but basically the use case is Tire.index('foobaz').aliases or Tire::Alias.all('foobaz') either gets the error