Process Summon search on demand when facets requested.

module/VuFind/src/VuFind/Search/Summon/Results.php

@@ -125,6 +125,11 @@ class Results extends \VuFind\Search\Base\Results
      */
     public function getFacetList($filter = null)
     {
+        // Make sure we have processed the search before proceeding:
+        if (null === $this->responseFacets) {
+            $this->performAndProcessSearch();
+        }
+
         // If there is no filter, we'll use all facets as the filter:
         $filter = is_null($filter)
             ? $this->getParams()->getFacetConfig()