Fix stale bandwidth-by-IP table entries

When the number of valid rows in the table reduced by more than 1 between updates, stale entries were left displayed at the end - e.g. 8 rows (0-7), then next update has only 5 rows (0-4). Row 5 is hidden but rows 6 and 7 remain displayed.
Merge pull request #469 from phil-davis/master

Fix stale bandwidth-by-IP table entries