UI: Fix transform options being wrongly enabled/disabled

They detection for this was not checking the n selected items but the
first n items in the list, which would lead to the options being enabled
or disabled based on the whether other items were locked.
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Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f