Followup ec785c2: re-evaluate clipping state after positioning

Calling .position() before and after showing in ec785c2 exposed
this bug: when we reposition the menu, its position relative to the
bottom of the screen has changed, so we need to reevaluate whether
it needs to be clipped.

Change-Id: I66a21ba647495d016e18198a9b3d0068b2de7915