blog MDL-23393 - Tidy up preferences form

Make form display set value and use mforms type checking

blog/preferences.php

@@ -73,6 +73,7 @@ require_capability('moodle/blog:view', $context);
 /// If data submitted, then process and store.
 
 $mform = new blog_preferences_form('preferences.php');
+$mform->set_data(array('pagesize' => get_user_preferences('blogpagesize')));
 
 if (!$mform->is_cancelled() && $data = $mform->get_data()) {
     $pagesize = $data->pagesize;

blog/preferences_form.php

@@ -39,7 +39,9 @@ class blog_preferences_form extends moodleform {
         $strpagesize = get_string('pagesize', 'blog');
 
         $mform->addElement('text', 'pagesize', $strpagesize);
-        $mform->setDefault('pagesize', get_user_preferences('pagesize'));
+        $mform->setType('pagesize', PARAM_INT);
+        $mform->addRule('pagesize', null, 'numeric', null, 'client');
+        $mform->setDefault('pagesize', 10);
 
         $this->add_action_buttons();
     }