Problem description: In Safari browser, an update of an existing value mapping created a new value mapping instead of actually updating the existing one. Furthermore, an empty error message is displayed in case if after such value mapping update the host/template is submitted:

Steps to reproduce:

1. Open Zabbix frontend in Safari browser
2. Create a host/template with a Value mapping
3. Open configuration of this host/template in edit mode and switch to "Value mapping" tab
4. Click on the existing value mapping name to open it's configuration form
5. In the configuration form change value of any field
6. Press "Update" button in Value mapping configuration form

Result: Instead of updating the existing value mapping, another value mapping is created. An empty error message is displayed if the user attempts to save such host/template configuration.
Expected: existing value mapping should be updated, no errors should be observed when attempting to save the host/template.

Example: