ListViews loses items if all visible items are removed.

ListViews loses items if all visible items are removed.

Occurs when at end of list and all visible items are removed in
multiple steps, without entering the event loop.
We were not updating visibleIndex if there were no visible items
when handling itemsRemoved().
Also avoid skipping items in refill if there are no valid visible
items for reference.

Change-Id: I2ff58fb191f6b053f33d5446220d597eb15b66d4
Task-number: QTBUG-19198
Reviewed-by: Bea Lam
(cherry picked from commit 576d577438f1193bbc934e904b809d5b23b8d54e)