Workaround loopfilter bug (in libvpx).

for UV loopfilter, skip odd row loopfilter if odd col loopfilter of
that same 8x8 pixel area was skipped also. This triggers, for example,
on the right side of vp90-2-02-size-66x66.webm; because the number of
cols is a not a multiple of 2, we skip the odd col loopfilter around
pixels at position x=68. However, because of a bug in libvpx, we have
to skip the row loopfilter around pixels at y=4, y=12, y=20 and y=28
(i.e. all odd rows) between x=64-68 also.

This fixes vp90-2-02-size-66x66.webm keyframe reconstruction to be
identical to what libvpx produces. Of vp90-2-02-*.webm, all files
except vp90-2-02-size-18x66.webm produce identical keyframe output
to libvpx now. vp90-2-03-size-*.webm still have several bugs.