Fix global-buffer-overflow in voAWB_Copy.

Copy() in frameworks/av/media/libstagefright/codecs/amrwbenc/src/util.c always
overreads the buffer by 4 bytes to the right, which, if we are very unlucky,
can even hit an unmapped memory page (in this case it is just a global
variable).

Bug: 22331081
Change-Id: I3d5d7f94c7248967518bf4d0faf34c364e431135