Added a couple of micro-optimizations to avoid calling wake() unnecessarily
and reduce JNI overhead slightly.
Fixed a minor issue where we were not clearing the "next" field of Messages
returned by the MessageQueue so the Message would hold on to its successor
and potentially prevent the GC from collecting it if the message were leaked
somehow.
Change-Id: I488d29417ce0cdd7d0e447cda76ec978ef7f811c
54e1cdacd2