fix(glpi_item): add default value to prevent error when field is not filled

[stonebuzz]

Add default value to prevent SQL error when field glpi_item is not filled

[2022-06-08 10:15:16] glpisqllog.ERROR: DBmysql::query() in /home/stanislas/Teclib/dev/GLPI/10.0-bugfixes/src/DBmysql.php line 370
  *** MySQL query error:
  SQL: INSERT INTO `glpi_plugin_fields_ticketbloc` (`plugin_fields_containers_id`, `items_id`, `plugin_fields_customdropdownfielddropdowns_id`, `nativetextfield`, `nativedatefield`, `nativedatetimefield`, `nativeyesnofield`, `nativeuserfield`) VALUES ('5', '10', '2', 'titi', '2022-06-07', '2022-06-07 10:14:42', '1', '2')
  Error: Field 'itemtype_glpiitemfield' doesn't have a default value
  Backtrace :
  src/DBmysql.php:1312                               
  src/CommonDBTM.php:705                             DBmysql->insert()
  src/CommonDBTM.php:1297                            CommonDBTM->addToDB()
  plugins/fields/inc/container.class.php:1068        CommonDBTM->add()
  plugins/fields/inc/container.class.php:1424        PluginFieldsContainer->updateFieldsValues()
  src/Plugin.php:1454                                PluginFieldsContainer::preItemUpdate()
  src/CommonDBTM.php:1563                            Plugin::doHook()
  front/ticket.form.php:84                           CommonDBTM->update()
  {"user":"2@Desktop","mem_usage":"0.006\", 4.37Mio)"} 

[AdrienClairembault]

Similar tables seems to use a null value instead of an empty string, here are two examples:

CREATE TABLE `glpi_items_devicegenerics` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `items_id` int(11) NOT NULL DEFAULT '0',
  `itemtype` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL,

CREATE TABLE `glpi_items_problems` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `problems_id` int(11) NOT NULL DEFAULT '0',
  `itemtype` varchar(100) COLLATE utf8_unicode_ci DEFAULT NULL,

[stonebuzz]

Similar tables seems to use a null value instead of an empty string, here are two examples:

CREATE TABLE `glpi_items_devicegenerics` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `items_id` int(11) NOT NULL DEFAULT '0',
  `itemtype` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL,

CREATE TABLE `glpi_items_problems` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `problems_id` int(11) NOT NULL DEFAULT '0',
  `itemtype` varchar(100) COLLATE utf8_unicode_ci DEFAULT NULL,

agree with that