Wrong height from Chaos::FHeightField::GetHeightAt()

1) Make a small 8x8 landscape

2) Set brush size = 10

3) Raise the heights of the 4 vertices inset (1, 1) from the corners. So just start at the corner, and move one in one cell from each corner, and increase that vertex's height.

4) Move the cursor on and off of the corner tiles. You can see that for some of them, the cursor position jumps a bit when you move from pointing at the tile to pointing next to it.