Fix bug where all apps scrollbar jumps.

The problem is that rowAppIndex is not being set when we swap in the
new predictions. So when we call AllAppsRecyclerView#getCurrentScrollY,
the "item.rowAppIndex == 0" clause returns true for every predicted app,
which results in a larger than expected value.

Bug: 64628968
Change-Id: I37ca660522b5a99666de2ea0b9c0aa8cd3732aca