Allow page view derived Advanced Search blocks on any page (#843)

* Allow page view derived Advanced Search blocks on any page

Allows the Advanced Search block to be used on pages
where its corresponding view is not present. Now it
will redirect to the route associated with the view
it was generated from.

This is not valid for Advanced Search blocks that
are derived from non-page based views, as there is
no known location in which to redirect the query.

* Fix for undefined index warning.

* Documented Exposed form style settings requirement for Advanced Search.

README.md

@@ -7,6 +7,7 @@
 - [Configuring Solr](#configuring-solr)
 - [Configure Collection Search](#configure-collection-search)
 - [Configure Views](#configure-views)
+  - [Exposed Form](#exposed-form)
   - [Collection Search](#collection-search)
   - [Paging](#paging)
   - [Sorting](#sorting)
@@ -96,6 +97,21 @@ the [Drupal Documentation](https://www.drupal.org/docs/8/core/modules/views), as
 well as the
 [Search API Documentation](https://www.drupal.org/docs/contributed-modules/search-api).
 
+### Exposed Form
+
+Solr views allow the user to configure an exposed form (_optionally as a
+block_). This form / block is **different** from the
+[Advanced Search Block](#advanced-search-block). This module does not make any
+changes to the form, but this form can cause the Advanced Search Block to not
+function if configured incorrectly.
+
+The Advanced Search Block requires that if present the Exposed forms
+`Exposed form style` is set to `Basic` rather than `Input Required`. As
+`Input Required` will prevent any search from occurring unless the user puts an
+additional query in the Exposed form as well.
+
+![Form Style](./docs/basic-input.png)
+
 ### Collection Search
 
 That being said it will be typical that you require the following
@@ -194,6 +210,11 @@ checkbox.
 
 ![image](./docs/advanced_search_block_settings.png)
 
+> N.B. Be aware that the Search views [Exposed Form](#exposed-form) can have an
+> affect on the function of the
+> [Advanced Search Block](#advanced-search-block). Please refer to that section
+> to learn more.
+
 ## Documentation
 
 Further documentation for this module is available on the