event: clear pending-state when re-arming timers

event: clear pending-state when re-arming timers

If a timer fires and is marked pending, but an application re-arms it
before it is dispatched, we now clear the pending state.

This fixes a bug where an application arms a timer, which fires and is
marked pending. But before it is dispatched, the application loses
interest in it and disables it. Now if the timer is re-armed and
re-enabled later, it will be immediately dispatched as it is still marked
pending.

This behavior is unexpected, so avoid it by clearing pending state when
re-arming timers. Note that applications have no way to clear pending
state themselves, so there's no current workaround.