Fix longpress crash.

The AllApps button doesn't usually accept longpresses, but
you can trick it into trying by holding one finger on it and
another on another icon in the hotseat. This patch defends
against that and bails out if the longpressed item has the
all apps rank (position in hotseat).

Bug: 11740833
Change-Id: I99785ccbc9e6dc6be2a9e56289b3cc0275fbb65c