Make sure an Array is returned from `__get_results_with_load`

Fixes the `undefined method `detect'` error when single record is returned from `__get_results_with_load`

If you use load: true when the search would return a single object it raises an error:

    NoMethodError:
    undefined method `detect' for #<--elastic search persistance model-->

This has been fixed before but it must have been lost when the code was refactored.

See also: <http://stackoverflow.com/questions/10592005/tire-gem-undefined-method-detect>

Related: #353

Closes #725