IllegalArgumentException in MagnificationGestureHandler

When enabling the magnifier feature it is possible to trigger
a system crash.

Problem:
On ACTION_DOWN a MESSAGE_ON_ACTION_TAP_AND_HOLD is sent to the
handler with a delay based on long-press timeout.  If the user
then removes their finger while outside of the magnification area,
(ACTION_UP) this message is not removed.  Then when the message
is handled on long-press timeout, it puts the state into
STATE_VIEWPORT_DRAGGING.  If the user then taps the screen again
it is handled by the StateViewportDraggingHandler resulting in:

 IllegalArgumentException: Unexpected event type: ACTION_DOWN

and a system server crash.

Bug: 65101895
Test: Manual:
1. Enable "Magnify with button" from accessibility settings
2. Tap accessibility button on the right navbar
3. Touch & hold bottom part of application area
4. Quickly drag down to the navbar and release
5. Touch anywhere
With this patch it should not crash

Change-Id: I7df8d2185f6db9d148d24d2b155cb357b3637a71