Change V and H intra prediction in lossless (TransformBypassModeFlag == 1)
macroblocks to correctly adhere to the specification. Affects lossless
encoding with 8x8dct or mix of lossless with normal macroblocks.

8x8dct has already been disabled in lossless mode for some time due to
being out-of-spec but this will allow us to re-enable it again.