PIE: Fix assistant issues

We should check if we have a search assistant any time pie is drawed, not
just on init. Also restore previous intent null check way instead of calling
SearchPanelView (may not be initialized yet at boot when pie and immersive are on).
Fix also an old bug, once activated for first time, on first google now swipe up
nothing happened (the check done at first init returned false).

Signed-off-by: Carlo Savignano <stevewatersy@gmail.com>