Fields which are marked as multiple can not be set to zero elements

Reproduction path:

1. Login to the cms
2. Go to the browse tab
3. Go to configuration
4. Go to hippo namespaces -> defaultcontent
5. Add new document type
6. Fill in name 'repeater'
7. Select 2 column
8. Finish
9. Add primitive field docbase
10. Mark multiple and ordered
11. Save
12. Update all content
13. Go to documents tab
14. Go to overview folder
15. Add new document of type 'repeater'
16. You will see that there is is a predefinied field already in the template
17. Click the delete
18. You will see that you can not set the repeater to 0 items.