Fix PathView not updating after all items are removed from the model.

Fix PathView not updating after all items are removed from the model.

Always clear the layoutScheduled flag on a refill even if there are no
items to create, otherwise future layouts won't be scheduled because
it appears one is already pending.

Fixes an issue in the dragselection example where items that should
have moved to the PathView instead disappeared.

Change-Id: I4302b5b43184c697a78f5c09dc3811326e2271ca
Reviewed-by: Martin Jones <martin.jones@nokia.com>