Update the layout when the wallpaper count changed

The wallpaper count in the collection could change dynamically
in rare case. And we should take it into the consideration
for the flexible layout feature(2 or 3 columns layout).

Bug: 191221570
Test: manual
Change-Id: Id70d2b8d61ed3aa4e537f02554c9171f20cf2c1a
1 file changed