Incorrect selection border when selection certain cell ranges

[ianscriven]

When selecting a large number of cells, the blue border around the selected cells doesn't always match the actual selected cells.

Steps to reproduce:

1. go to https://demo.vaadin.com/spreadsheet/
2. select cell A2
3. Scroll down to row 100
4. Shift-click cell A100 to select range A2:A100
5. All selected cells are shaded blue, but the blue border stops after cell A98

If you start by selected cell A1 (instead of A2) it all works fine.