Exposed filters crashes if Solr Index is disabled

Problem/Motivation

If you have a site that doesn't have Solr search setup, but is using the exposed filters view. The results will come back as Null and return an error inside the the facets_exposed_filters_views_post_execute().

I know this probably doesn't happen very often, but my default Solr Index is disabled locally and this causes every page to crash.

Steps to reproduce

1. Setup Solr and Solr index with fields
2. Create a view with facets exposed form
3. Add views exposed filter block to all pages
4. Disable Solr Index
5. Go to the front page

Proposed resolution

Just need to check if the search results return Null.

Remaining tasks

N/A

User interface changes

N/A

API changes

N/A

Data model changes

N/A