Add More CellMap Range Checks

When rotating, zooming, and interacting with a model, the cellmap will rarely and randomly be empty even though the cell map sizes will be properly calculated. By adding extra guard conditions, for the frames which are not correctly calculated we will not crash with the out of range accesses.

While not an ideal fix, as this code is called frequently enough, and any issues will disappear with the next valid render, the chances of a user getting a bad render and noticing is not likely.