Can't add already registered badge to vendor application

[jtatum]

Steps to reproduce:

1. Edit a vendor application
2. Click "Add" to add a badge
3. Click "select" to select an attendee ID
4. Select an attendee

Expected result: form populates with attendee data and can be saved
Actual result: attendee ID populated, but no other data and form can't be saved: "Save failed. Please try again."

Looks like it just needs to fill in the missing attendee data.