This fixes an issue where an `unselect` event would be incorrectly
triggered when the selected option was selected again in a single
select. This has been fixed now, so the even will only be triggered
for multiple selects. The `close` event will still be triggered
though, so the functionality will still remain the same to the user.
This closes https://github.com/select2/select2/issues/2959.
981c4065af