Fix validation of local application submissions that belong to more than one category.

Previously, the interface for adding an application failed when selecting more than one category for an application. This should fix the validation function that was causing the problem.

To test:
1. click on Applications->Add after running through the setup wizard.
2. Add an application and select more than one category for it (for instance both 'Community' and 'Fun').
3. If you are able to submit the application and it returns you to the list of applications on this node, then this fix works.