Smarter handling of unexpected Combined/SearchBox params.

module/VuFind/src/VuFind/Controller/CombinedController.php

@@ -244,7 +244,14 @@ class CombinedController extends AbstractSearch
             $lookfor = $this->params()->fromQuery('lookfor');
             return $this->redirect()->toUrl($target . urlencode($lookfor));
         default:
-            throw new \Exception('Unexpected search type.');
+            // If parameters are completely missing, just redirect to home instead
+            // of throwing an error; this is possibly a misbehaving crawler that
+            // followed the SearchBox URL without passing any parameters.
+            if (empty($type) && empty($target)) {
+                return $this->redirect()->toRoute('home');
+            }
+            // If we have a weird value here, report it as an Exception:
+            throw new \Exception('Unexpected search type: "' . $type . '".');
         }
     }