Drop touch events when no window was touched.

Prevent spurious ANRs in the case where an input event is simply
undeliverable because there is no window at the touched location.
Previously, we would assume that we were just waiting for an
application to start and become available to handle the event but
this assumption is no longer valid.

Monkeys in particular have a tendency to inject events outside
of the boundaries of the display which results in spurious ANRs.
So we should just reject them.

Bug: 9774124
Change-Id: I5c40ce4c942f0557593a229dc5253a0e0bdb8466