folderview: Fix grid overflow property so it properly reports overflow state
In some cases, viewportArea.widthRatio or heightRatio can be 0 when it's not actually overflowing. So account for that to ensure we properly report the overflow state.
In some cases, viewportArea.widthRatio or heightRatio can be 0 when it's not actually overflowing. So account for that to ensure we properly report the overflow state.