KPropertiesDialog: Update enabled state and handle non-existing file type in default handler label
The dialog updates live as Sycoca processes mime changes. If a new file type is created, the label text and icon was updated but it was not enabled.
Also show "No registered file type" and change the button to say "Create..." since clicking it will create a new custom "x-kdeuser" file type, and not edit any existing associations.
Edited by Kai Uwe Broulik