Fix flaky RuntimeException in CellLayout.

Changing the grid while a previous loader is running (more likely to happen in test) can cause a saved item info to have a cell position outside the bounds of the new grid. This should just be handled the same way as other item infos being loaded in an occupied space.

Flag: not needed
Fixes: 233989158
Test: changed grid sizes multiple times
Change-Id: Ibba337c224e7a08533331a87b1369ebf96e3c9a3