Make ParamBag Countable.

- Fixes PHP 7.2 compatibility.

module/VuFindSearch/src/VuFindSearch/ParamBag.php

@@ -41,7 +41,7 @@ namespace VuFindSearch;
  * @license  http://opensource.org/licenses/gpl-2.0.php GNU General Public License
  * @link     https://vufind.org
  */
-class ParamBag
+class ParamBag implements \Countable
 {
     /**
      * Parameters
@@ -76,6 +76,16 @@ class ParamBag
         return isset($this->params[$name]) ? $this->params[$name] : null;
     }
 
+    /**
+     * Count parameters in internal array. Needed for Countable interface.
+     *
+     * @return int
+     */
+    public function count()
+    {
+        return count($this->params);
+    }
+
     /**
      * Return true if the bag contains any value(s) for the specified parameter.
      *