Navigation in grid does not behave correctly: Prevented from moving down if no item directly below highlight

[retrocaster]

If you have a grid with no item directly below your current selection then pressing down on the directional pad does nothing.

For example, if I have a Watch Later feed that's displayed as the following grid of six videos (labeled 1 through 6):

1 2 3 4 5 6

And I'm currently highlighting 3 and press down, nothing will happen. Similarly, if I'm currently highlighting 4 and press down, nothing will happen. Both of these cases should cause 6 to be highlighted. In other words, if there's at least one item in the row below and you press down with no item directly below your current item then it should move the highlight to the right-most item in the row below.