Fix to CEHorizontalSwipeInteractionController when UIPanGestureRecognizer translation.x == 0

Sometimes handleGesture: incorrectly sets the BOOL rightToLeftSwipe to
false when it should be true…This is due to [gestureRecognizer
translationInView:gestureRecognizer.view.superview] sporadically
returning {0, 0}; usually this occurs when making slow, methodical
movement swipes while starting at center of view window.  Solution is
to break anytime {0, 0} is returned (where translation.x == 0) so that
nothing happens.
Added a few comments