Bubbles: fix some issues with the pointer

* Pointer was missing if showing vertically on the right
  side, this is fixed & tried to make the code a lil more
  clear
* Pointer was missing for the bubble overflow, this is
  also fixed

Bug: 181888630
Test: manual - make sure the pointer is visible when the
               stack is expanded, check landscape left &
               right on small & large screen and check
               portrait on phone.
Change-Id: Id7dc6ae9a1f3e798940342b780940fb77ceaed3a