1. AccessibilityInput filter was not checking whether the touch
explorer instance is not null before passing it an accessibility
event. If the accessibility event is dispatched before the input
filter is installed but after it is created we runt into this
case.
2. Added a missing null check in accessibility node info.
bug:6635089
Change-Id: Ia389dc1f427427eb73794f6331ccb870e0b44c55