applets/kicker: fix arrow down from search field to column

Amends 8746d41e

When displaying runner columns, Kicker initially highlights the first entry of the first column even while focus is still on the search field, as pressing return will activate that entry immediately. Previously, pressing down from the search field would skip the already highlighted entry and move to the second element in the first column. During the keyboard navigation refactoring, this special case was not correctly handled. This makes pressing arrow down feel as if nothing happens, as the selection does not change (something does happen, focus moves from the search field to the search results, but this is a distinction with little immediate difference).

This change adds special handling for this case, restoring behavior back to how it worked for 6.4.