No good reason to be tricky here. I don't know why 'break' occurred to me
as the natrual replacement for the 'return', but an if/else block is
definitely clearer.

Change-Id: I08a336307afeb0dc7efa494b37398f239f66c2cf

The new scheme introduced in I68d35a2f did not clamp chroma MVs in the SPLITMV
 case, and clamped them incorrectly (to the luma plane bounds) in every other
 case.
Because chroma MVs are computed from the luma MVs before clamping occurs, they
 could still point outside of the frame buffer and cause crashes.
This clamping happens outside of the MV prediction loop, and so should not
 affect bitstream decoding.

This patch removes the secondary MV clamping from the MV decoder. This
behavior was consistent with limits placed on non-split MVs by the
reference encoder, but was inconsistent with the MVs generated in the
split case.

The purpose of this secondary clamping was only to prevent crashes on
invalid data. It was not intended to be a behaviour an encoder could or
should rely on. Instead of doing additional clamping in a way that
changes the entropy context, the secondary clamp is removed and the
border handling is made implmentation specific. With respect to the
spec, the border is treated as essentially infinite, limited only by
the clamping performed on the near/nearest reference and the maximum
encodable magnitude of the residual MV.

This does not affect any currently produced streams.

Change-Id: I68d35a2fbb51570d6569eab4ad233961405230a3

Change-Id: Ieebea089095d9073b3a94932791099f614ce120c