[5.4] Fix MySql 8 error "Illegal argument to a regular expression." in banners model (#46547)

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Co-authored-by: Richard Fath <richard67@users.noreply.github.com>

Author: beni71

components/com_banners/src/Model/BannersModel.php

@@ -186,14 +186,14 @@ protected function getListQuery()
             } else {
                 $temp   = [];
                 $config = ComponentHelper::getParams('com_banners');
-                $prefix = $config->get('metakey_prefix');
+                $prefix = $config->get('metakey_prefix', '');
 
                 if ($categoryId) {
                     $query->join('LEFT', $db->quoteName('#__categories', 'cat'), $db->quoteName('a.catid') . ' = ' . $db->quoteName('cat.id'));
                 }
 
                 foreach ($keywords as $key => $keyword) {
-                    $regexp       = '[[:<:]]' . $keyword . '[[:>:]]';
+                    $regexp       = $db->getServerType() === 'mysql' ? '\\b' . $keyword . '\\b' : '[[:<:]]' . $keyword . '[[:>:]]';
                     $valuesToBind = [$keyword, $keyword, $regexp];
 
                     if ($cid) {
@@ -272,8 +272,10 @@ public function getItems()
         if (!isset($this->cache['items'])) {
             $this->cache['items'] = parent::getItems();
 
-            foreach ($this->cache['items'] as &$item) {
-                $item->params = new Registry($item->params);
+            if (\is_array($this->cache['items'])) {
+                foreach ($this->cache['items'] as &$item) {
+                    $item->params = new Registry($item->params);
+                }
             }
         }