MDL-41819 try to work around max_input_vars restriction

backup/util/ui/base_moodleform.class.php

@@ -73,6 +73,11 @@ abstract class base_moodleform extends moodleform {
      */
     function __construct(base_ui_stage $uistage, $action=null, $customdata=null, $method='post', $target='', $attributes=null, $editable=true) {
         $this->uistage = $uistage;
+        $attributes = (array)$attributes;
+        if (!isset($attributes['enctype'])) {
+            $attributes['enctype'] = 'application/x-www-form-urlencoded'; // Enforce compatibility with our max_input_vars hack.
+        }
+
         parent::__construct($action, $customdata, $method, $target, $attributes, $editable);
     }
     /**

backup/util/ui/restore_ui_stage.class.php

@@ -697,6 +697,7 @@ class restore_ui_stage_process extends restore_ui_stage {
         $html .= html_writer::start_tag('form', array(
             'action'    => $url->out_omit_querystring(),
             'class'     => 'backup-restore',
+            'enctype'   => 'application/x-www-form-urlencoded', // Enforce compatibility with our max_input_vars hack.
             'method'    => 'post'));
         foreach ($url->params() as $name => $value) {
             $html .= html_writer::empty_tag('input', array(