Bug 16727: Clarify upload category note

Bug 16727: Clarify upload category note

This patch clarifies the note on the upload tool
that states that no categories are defined.

To test:

* Log in to Koha
* Confirm that you have no values set for the UPLOAD
  authorized value category
* Visit Tools > Upload
* Check the warning note for typos
* Add a authorized value category for UPLOAD
* Visit Tools > Upload
* Confirm that note is replaced

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>

Signed-off-by: Brendan Gallagher <brendan@bywatersolutions.com>