MDL-33682 backup: cope with sections called '0'

It was not previously possible to have a section called 0 because of
bugs in the standard course formats, but we hit this with the OU course
format. You got an exception because backup settings tested to see if
their lable was empty, which means a section name of '0' was fatal.
Should work now.

backup/backup.php

@@ -62,7 +62,7 @@
     case backup::TYPE_1SECTION :
         $coursecontext = get_context_instance(CONTEXT_COURSE, $course->id);
         require_capability('moodle/backup:backupsection', $coursecontext);
-        if (!empty($section->name)) {
+        if ((string)$section->name !== '') {
             $sectionname = format_string($section->name, true, array('context' => $coursecontext));
             $heading = get_string('backupsection', 'backup', $sectionname);
             $PAGE->navbar->add($sectionname);

backup/moodle2/restore_stepslib.php

@@ -1083,7 +1083,7 @@ public function process_section($data) {
         // Section exists, update non-empty information
         } else {
             $section->id = $secrec->id;
-            if (empty($secrec->name)) {
+            if ((string)$secrec->name === '') {
                 $section->name = $data->name;
             }
             if (empty($secrec->summary)) {

backup/util/factories/backup_factory.class.php

@@ -139,7 +139,7 @@ public static function get_backup_section_task($format, $sectionid) {
             throw new backup_task_exception('section_task_section_not_found', $sectionid);
         }
 
-        return new backup_section_task(empty($section->name) ? $section->section : $section->name, $sectionid);
+        return new backup_section_task((string)$section->name !== '' ? $section->section : $section->name, $sectionid);
     }
 
     /**

backup/util/ui/backup_ui_setting.class.php

@@ -129,7 +129,7 @@ public function get_static_value() {
      * @param string $label
      */
     public function set_label($label) {
-        if (empty($label) || $label !== clean_param($label, PARAM_TEXT)) {
+        if ((string)$label === '' || $label !== clean_param($label, PARAM_TEXT)) {
             throw new base_setting_ui_exception('setting_invalid_ui_label');
         }
         $this->label = $label;