Add a logic to check startpos equality first on focus navigation

Add a logic to check startpos equality first on focus navigation

The previous logic for checking next-button-to-be-highlighted
when a direction key is pressed, put more emphasis on the length
of overlapping height (in horizontal movement case) when looking
for a possible candidate.
But when an adjacent button has smaller overlapping height value
but has identical ypos, it would be much suitable to choose it
as next highlighted item, than to an item whose overlapping
height is bigger but is in farther location.
So, changed code not to reset candidate_distance_x when the
ypos of current possible candidate is identical to that of
currently highlighted button.

Change-Id: I0d763f42334b76b3ff109cb89c170f9fb62aa1ab