Fix a bug where the last large task index was not being set correctly.

This was causing the focused task shift to be calculated incorrectly, which was resulting in the focused task being shifted too far to the left.


Bug: 330342294
Fix: 371490320
Flag: com.android.launcher3.enable_large_desktop_windowing_tile
Test: Manual. Open 1 DesktopTask, 1 FocusedTask, 2 other tasks in the grid. Dismiss the focused task. The rebalance should work keeping the new focused task next to desktop task.
Change-Id: If6f95814942c2cbadc30a0082649569f21dea60a