altoslib: Stop reflective JSON class walk at Object instead of null

altoslib: Stop reflective JSON class walk at Object instead of null

Android has classes above Object which are all tied together which
cause the object walking to fail in pretty spectacular ways. As Object
has no interesting fields, that serves as a fine barrier to the super
class walk and works on both android and real java.

Signed-off-by: Keith Packard <keithp@keithp.com>