MDL-36795 - lib / administration: maxsections now limits the default setting for numsections.

In the default course settings, setting the maximum number topics / weeks  to 0 would not
change the default number of sections on the same page as any other number would.
A more appropriate check has been put in place.

This also incorporates a fix for MDL-28584. The course edit screen now also checks to see
if maxsections is set or numeric. If it is not set or numeric then it defaults to 52.

lib/adminlib.php

@@ -3818,7 +3818,7 @@ class admin_settings_num_course_sections extends admin_setting_configselect {
     /** Lazy-load the available choices for the select box */
     public function load_choices() {
         $max = get_config('moodlecourse', 'maxsections');
-        if (empty($max)) {
+        if (!isset($max) || !is_numeric($max)) {
             $max = 52;
         }
         for ($i = 0; $i <= $max; $i++) {