swscale/swscale_unscaled: Fix odd height inputs for bayer_to_yv12_wrapper()

Fixes: 372d2df1f04b49e25f109f07f90b1505/asan_heap-oob_2835d2e_8501_99e0114d7ba3a6db885d0b4684d200c1.cine
Fixes out of array read

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
