Can't load index with prefix_default_locale

[MaxLap]

If using prefix_default_locale, the index cannot be loaded because the index has a default locale of "en", so ends up located at "/en/bridgetown_quick_search/index.json"

This ens up being similar to #28.

I realize that maybe the page could contain the url to the desired index. This would make it possible to solve this issue as well as #28 and would be a good part of the way to solve #29 all at once.