Row virtualization is working incorrectly in expandable grid

[czyzm]

When using expandable grid the row virtualization is not taking into account that rows may be expanded. If any row is expanded, the additional space is left at the end of the grid. If last row is expanded, the expanded data may be not visible.

Steps to reproduce:

1. Go to expandable example (http://ui-grid.info/docs/#!/tutorial/216_expandable_grid)
2. Expand some rows in the first grid and scroll to the bottom - empty space is added.

Can confirm I'm running into this issue as well. I've had to essentially force my grid to render way too much by abusing minRowsToShow, scrollThreshold, and excessRows to avoid this issue, at a huge cost of speed.

[vance]

#5395

[vance]

it renders based only on the count and not the computed height. including the expandable row. this PR fixes it. the automated code checker says it's too complex though, so uh...