Blog Plugin: fix for notice

plugins/blog/blog.plugin.php

@@ -109,8 +109,10 @@ class Blog {
         }
     
         foreach($posts as $post) {
+            if (isset($post['tags'])) {
                 $tags_string .= $post['tags'].',';
             }
+        }
 
         $tags_string = substr($tags_string, 0, strlen($tags_string)-1);