Fixes a crash in the AllAppsFastScrollHelper where on updating the activated flag

on the views it was trying to retrieve an item from the model for a non-existing
position in the model.

The fix is to check the position to the model size. It's not clear in what circumstance
the model (ArrayList) can differ to the position returned from the view-holder's
getAdapterPosition().

Bug: 36176501

Change-Id: I01b8daaad884702f9ed0e1caaa03d0ebaca69d39