MDL-66032 badges: Prevent empty awarded badges criteria being created.

When creating or editing the awarded badges criteria, the select element should be
required to prevent empty criteria from being created. In addition, if there are
already badges created with the empty criteria, there should be not be an exception
thrown when assessing whether the criteria has been completed.

badges/criteria/award_criteria_badge.php

@@ -112,7 +112,7 @@ public function get_options(&$mform) {
             if ($this->id !== 0) {
                 $selected = array_keys($this->params);
             }
-            $settings = array('multiple' => 'multiple', 'size' => 20, 'class' => 'selectbadge');
+            $settings = array('multiple' => 'multiple', 'size' => 20, 'class' => 'selectbadge', 'required' => 'required');
             $mform->addElement('select', 'badge_badges', get_string('addbadge', 'badges'), $select, $settings);
             $mform->addRule('badge_badges', get_string('requiredbadge', 'badges'), 'required');
             $mform->addHelpButton('badge_badges', 'addbadge', 'badges');
@@ -243,7 +243,6 @@ public function get_completed_criteria_sql() {
         if ($this->method == BADGE_CRITERIA_AGGREGATION_ANY) {
             // User has received ANY of the required badges.
             $join = " LEFT JOIN {badge_issued} bi2 ON bi2.userid = u.id";
-            $where = "AND (";
             $i = 0;
             foreach ($this->params as $param) {
                 if ($i == 0) {
@@ -254,7 +253,10 @@ public function get_completed_criteria_sql() {
                 $params['badgeid'.$i] = $param['badge'];
                 $i++;
             }
-            $where .= ") ";
+            // MDL-66032 Do not create expression if there are no badges in criteria.
+            if (!empty($where)) {
+                $where = ' AND (' . $where . ') ';
+            }
             return array($join, $where, $params);
         } else {
             // User has received ALL of the required badges.