Creation Restrictions shouldn't allow adding duplicate locations

Steps to reproduce

1. Login as Admin
2. Go to Administer Wiki > Content > Page Templates
3. Write a "Template Provider" name in the Title field
4. Click on 'Create' button
5. Under Creation Restrictions select a location e.g. 'Home'
6. Click "+" and add again the same location e.g. 'Home'

Expected results

The location is displayed a single time in the list of locations.

Actual results

The location is duplicated, being displayed as many times as it's being added.

The same issue can be reproduced when creating an AppWithinMinutes for ex. at Step 3 under "Where to create entries" section.

I've also reproduced this on XWiki 16.4.2, 16.6.0 and 11.10.13, but it may be reproducible on older versions as well.