Fix NPE in InputManagerCallback#notifyFocusChanged

The newToken may be null from InputDispatcher before the
next focused window is ready.

Bug: 134365580
Test: Launch any activity and no error log of InputManager-JNI.
Test: atest PointerCaptureTest WindowFocusTests
Change-Id: Ifbb08a551a1ab1d3db536f4708164dbe965ac43b
1 file changed