Fix: End handle disappears when the selection is short.

HandleView#isVisible didn't use getHorizontalOffset; thus,
the position is always computed as if Gravity.LEFT is set.
As a result, isVisible can be wrongly false for the end
handle and the handle is dismissed.

Bug: 20480054
Change-Id: Ib3242000bb98ae28e0cb37bf5b05069754abbfc6