libbinder_ndk: log on null non-@nullable fd/binder

b/c the NDK backend C++ types can actually contain the null value, it's
not clear from the type system alone that these cannot be null or why.

Bug: 176177197
Test: with `atest CtsNdkBinderTestCases`
12-23 02:18:12.891 29957 29979 E android.binder.cts: Passing null binder
object as non-@nullable AIDL IBinder
12-23 02:18:12.902 29957 29979 E android.binder.cts: Passing -1 file
descriptor as non-@nullable AIDL ParcelFileDescriptor
12-23 02:18:13.149 29957 29979 E android.binder.cts: Passing null binder
object as non-@nullable AIDL IBinder
12-23 02:18:13.160 29957 29979 E android.binder.cts: Passing -1 file
descriptor as non-@nullable AIDL ParcelFileDescriptor
12-23 02:18:13.282 29957 29979 E android.binder.cts: Passing null binder
object as non-@nullable AIDL IBinder
12-23 02:18:13.295 29957 29979 E android.binder.cts: Passing -1 file
descriptor as non-@nullable AIDL ParcelFileDescriptor
12-23 02:18:13.452 29957 29979 E android.binder.cts: Passing null binder
object as non-@nullable AIDL IBinder
12-23 02:18:13.465 29957 29979 E android.binder.cts: Passing -1 file
descriptor as non-@nullable AIDL ParcelFileDescriptor
12-23 02:18:13.621 29957 29979 E android.binder.cts: Passing null binder
object as non-@nullable AIDL IBinder
12-23 02:18:13.634 29957 29979 E android.binder.cts: Passing -1 file
descriptor as non-@nullable AIDL ParcelFileDescriptor

Change-Id: Ic855aa85d95724e82c46e941b442ff6cbba39e77