swscale/yuv2rgb: Increase YUV2RGB table headroom

This makes SWS more robust
Fixes: 07650a772d98aa63b0fed6370dc89037/asan_heap-oob_27ddeaf_2657_2c81ff264dee5d9712cb3251fb9c3bbb.264
Fixes: out of array read

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