Fix missing form data when multi-select empty

[cconard96]

Q	A
Bug fix?	yes
New feature?	no
BC breaks?	no
Deprecations?	no
Tests pass?	yes
Fixed tickets	-

When a multiple-select dropdown has no options selected, no form data is sent to GLPI so that field is ignored. This made it impossible to handle removing all selections from a dropdown unless the missing field was treated specially as if it were an empty selection. That special handling is not correct though as partial updates via the API(s) are possible and failing to specify a multiselect field in an API update request should not delete the value.

The fix adds a hidden input with the same name just before the select element in the DOM. If the browser decides to send the data for the select, the hidden input is ignored.

This may cause some breaks besides the one I found immediately for the devices_in_menu config options. On some other dropdowns it seemed to work without issue. Other cases may be found as work on the UI continues, during beta testing, or through added E2E tests.

[cedric-anne]

You can detect existing hack by searching for exportArrayToDB() usage preceded by a isset() on an input with a different key. For instance:

        if (isset($input["_helpdesk_item_types"])) {
            if ((!isset($input["helpdesk_item_type"])) || (!is_array($input["helpdesk_item_type"]))) {
                $input["helpdesk_item_type"] = [];
            }
           // Linear_HIT: $input["helpdesk_item_type"] = array_keys($input["helpdesk_item_type"]
            $input["helpdesk_item_type"] = exportArrayToDB($input["helpdesk_item_type"]);
        }

helpdesk_item_type is used only if _helpdesk_item_types is set.