overview: rebalance hidden tasks in grid

The tasks that are not showing in the screen will be rearranged. This
doesn't change anything for tasks before the dismissed task because the
grid is already balanced there.

Fixes: 194189955
Test: manual with 10 tasks, normal and RTL mode
Change-Id: I07ddbb752110339751bd1ed6056fe9f645b5497f
1 file changed