Check if item is selectable before calling on click

This CL fixes a bug in ListView where it might call onClick on an
un-clickable if a new touch arrives before up timeout.

We could actually consider making child position non-changable
but that will change behavior. This seems safer approach.

Bug: 27198796
Change-Id: I7b15d04efa19d1d760a294bd027f3da3aaa3a445