fix for adbd pinning CPU

adbd was spinning between select & read (0 bytes) for an adb_auth
socket.  The read documentation states: "On success, the number of
bytes read is returned (zero indicates end of file)" so the code has
been modified to close the connection (like the read error case).

BUG=17419868

Change-Id: I1d8fb70c8e1876225ba8d47ea0a2b6265a7d182b