[dash] Keyboard focus can move to empty search results page

[Gerry Boland]

In the Dash, if you perform a search which returns zero results, pressing down allows you to navigate away from the inputbox, but to nothing.

Steps to Repro
-------------------------
1. Bring up Dash
2. Enter search term which returns zero results
3. Press the down key. Press it again.

Expected Result
---------------------------
Focus remains with the input box

Actual Result
---------------------------
Focus goes away from the input box.