ArrayIndexOutOfBounds exception in TouchExplorer.

1. The explorer was injecting up/down touch events to
   click with the id of the last pointer that went up
   but the prototype i.e. last touch explore event may
   not contain this pointer. Since we click on the last
   touch explored location then using the action pointer
   index of that event is the right approach.

bug:4551506

Change-Id: I73428b09dc014417096a52e667f58768a2871dc8