PIE: Fix random showing of navbar when swiping from top.

We need to condition here aswell to be sure top swipe doesn't trigger up
navbar at all even if we set its height to 0 is an useless call.

Addressing JIRA AOSPA-151 issue.

Signed-off-by: Carlo Savignano <stevewatersy@gmail.com>
Merge branch 'pa_upstream/kitkat'