fix(ldapfield): missing post value when field fails to populate

Signed-off-by: btry <tbugier@teclib.com>

Author: btry

inc/fields/ldapselectfield.class.php

@@ -187,6 +187,9 @@ public static function getJSFields() {
 
    public function parseAnswerValues($input) {
       $key = 'formcreator_field_' . $this->fields['id'];
+      if (!isset($input[$key])) {
+         $input[$key] = '';
+      }
       if (!is_string($input[$key])) {
          return false;
       }