Adding new tags batch manager single mode

[HWFord]

With the new single mode batch manager, if we want to add a new tag the interface lets us think we can create a new one. However if we click on save and refresh the page the tag no longer exists. When checking the tag manager the tag we "just created" doesn't exist.

In Piwigo 14 with the old single mode, this functionnality works, we can add new tags.